Therapeutic compounds

ABSTRACT

The invention relates to a method of improving oral drug absorption of adenosine analogues by the use of 2′-methoxy adenosine pro-drugs and to the use of these pro-drugs as medicaments. The invention further relates to compounds that are pro-drugs of adenosine receptor agonists, and to their use as therapeutic compounds, in particular as analgesic or anti-inflammatory compounds, or as disease modifying antirheumatic drugs (DMARDs), and to methods of preventing, treating or ameliorating pain or inflammation using these compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of Swedish application No. 0601397-3filed Jun. 27, 2006 and U.S. application 60/837,402 filed Aug. 11, 2006,the entire contents of each is herein incorporated by reference.

TECHNICAL FIELD

The invention relates to a method of improving oral drug absorption ofadenosine analogues by the use of 2′-methoxy adenosine pro-drugs and tothe use of these pro-drugs as medicaments. The invention further relatesto compounds that are pro-drugs of adenosine receptor agonists, and totheir use as therapeutic compounds, in particular as analgesic oranti-inflammatory compounds, or as disease modifying antirheumatic drugs(DMARDs), and to methods of preventing, treating or ameliorating pain orinflammation using these compounds.

BACKGROUND ART

Adenosine is a ubiquitous local hormone/neurotransmitter that acts onfour known receptors, the adenosine A1, A2A, A2B and A3 receptors.Adenosine generally serves to balance the supply and demand of energy intissues. For example, in the heart released adenosine slows the heart byan A1 receptor mediated action in the nodes and atria (Belardinelli, L &Isenberg, G Am. J. Physiol. 224, H734-H737), while simultaneouslydilating the coronary artery to increase energy (i.e. glucose, fat andoxygen) supply (Knabb et al, Circ. Res. (1983) 53, 33-41). Similarly,during inflammation adenosine serves to inhibit inflammatory activity,while in conditions of excessive nerve activity (e.g. epilepsy)adenosine inhibits nerve firing (Klitgaard et al, Eur J. Pharmacol.(1993) 242, 221-228). This system, or a variant on it, is present in alltissues.

Adenosine itself can be used to diagnose and treat supraventriculartachycardia. Adenosine A1 receptor agonists are known to act as powerfulanalgesics (Sawynok, J. Eur J Pharmacol. (1998) 347, 1-11; Giffin et al,(2003) 23, 4, 287-292). A2a agonists have recently been shown to givesignificant pain relief in conditions of increased pain sensitivity(such as neuropathic and inflammatory hyperalgesia) (WO 2004/052377; WO2004/078183; WO 2004/078184; WO 2005/084653) and are known to haveanti-inflammatory activity (see, for example U.S. Pat. No. 5,877,180; WO99/34804; Linden et al, Expert Opin. Investig. Drugs (2005) 14, 7,797-806; Sitkovsky et al, TRENDS in Immunology (2005) 26, 6, 299-304;Linden et al, Journal of Immunology (2006) 117, 2765-2769; Cronstein etal (2004) 25, 1, 33-39). In experimental animals, A2A receptor agonistshave been shown to be effective against a wide variety of conditionsincluding sepsis (Linden et al, The Journal of Infectious Diseases(2004) 189, 1897-1904), arthritis (Cohen et al, J. Orthop. Res. (2005)23, 5, 1172-1178; Cohen et al, J. Orthop. Res. (2004) 22, 2, 427-435),and ischaemia/reperfusion injury arising from renal, coronary orcerebral artery occlusion (see, for example Day et al, J. Clin. Invest,(2003) 112, 883-891; Linden et al, Am. J. Physiol. Gastrointest. LiverPhysiol. (2004) 286, G285-G293; Linden et al, Am J. Physiol. (1999) 277,F404-F412; Schlack et al, J. Cardiovasc. Pharmacol. (1993) 22, 89-96; Zuet al, J. Cardiovasc. Pharmacol. (2005) 46, 6, 794-802; Linden et al, AmJ. Physiol. Heart Circ. Physiol. (2005) 288, 1851-1858; Kennedy et al,Current Opinion in Investigational Drugs (2006) 7, 3, 229-242). Thecommon factor in these conditions is a reduction in the inflammatoryresponse caused by the inhibitory effect of this receptor on most, ifnot all, inflammatory cells. A2a agonists are also known to promotewound healing (Montesinos, Am. J. Pathol. (2002) 160, 2009-2018).

However, the ubiquitous distribution of adenosine receptors means thatadministration of adenosine receptor agonists causes adverse sideeffects. This has generally precluded the development of adenosine-basedtherapies. Selective A1 receptor agonists cause bradycardia. A2Areceptor agonists cause widespread vasodilation with consequenthypotension and tachycardia. The first selective A2A receptor agonist(2-[4-(2-carboxyethyl)phenylethylamino]-5′-N-ethylcarboxamidoadenosine,or CGS21680), was tested in a Phase 2A clinical trial as a potentialanti-hypertensive. However, administration of this compound caused alarge fall in blood pressure and consequent increase in cardiac output.This has prevented use of CGS21680 as a medicament. Webb et al. (J.Pharmacol Exp Ther (1991) 259, 1203-1212), Casati et al, (J PharmacolExp Ther (1995) 275(2):914-919), and Bonnizone et al, (Hypertension.(1995) 25, 564-9) show that selective A2A adenosine receptor agonistscause hypotension and tachycardia. The degree of tachycardia induced issufficient to preclude their use as medicaments. Alberti et al, (JCardiovasc Pharmacol. (1997) September; 30(3):320-4) discloses thatselective A2A adenosine receptor agonists are potent vasodilators thatreduce blood pressure and induce marked increments in heart rate andplasma renin activity. These side effects preclude their use asmedicaments.

U.S. Pat. No. 5,877,180 relates to agonists of A2A adenosine receptorswhich are stated to be effective for the treatment of inflammatorydiseases. The preferred agonists, WRC0090 and SHA 211 (WRC0474), aredisclosed to be more potent and selective than previously reportedadenosine analogs such as CGS21680 and CV1808. Administration of SHA 211or WRC0090 is considered to reduce the possibility of side effectsmediated by the binding of the analogs to other adenosine receptors.However, only in vitro data relating to the activity of SHA 211 isincluded. There is no demonstration that any of the compounds describedcould be therapeutically effective in vivo without causing serious sideeffects. Although side effects mediated by the binding of potent andselective adenosine A2A receptor agonists to other adenosine receptorsis expected to be reduced by use of such agonists, the ubiquitousdistribution of adenosine receptors means that these compounds wouldstill be expected to activate adenosine A2A receptors in normal tissueand, therefore, cause serious side effects (such as hypotension andreflex tachycardia).

U.S. Pat. No. 3,936,439 discloses use of 2,6-diaminonebularinederivatives as coronary dilating and/or platelet aggregation inhibitoryagents for mammals. In vivo data in dogs is included to support thecoronary dilating action of N²-Phenyl-2,6-diaminonebularine,N²-Cyclohexyl-2,6-diaminonebularine,N²-(p-methoxyphenyl)-2,6-diaminonebularine, andN²-Ethyl-2,6-diaminonebularine, and in vitro data supports the plateletaggregation inhibitory action of N²-Phenyl-2,6-diaminonebularine,N²-cyclohexyl-2,6-diaminonebularine, 2,6-Diaminonebularine, andN²-Ethyl-2,6-diaminonebularine. FR 2162128 (Takeda Chemical Industries,Ltd) discloses that adenosine derivatives (including 2-alkoxy adenosinederivatives comprising a lower alkyl group of not less than two carbonatoms) have hypotensive and coronary vasodilatory activity. In vivo datain dogs supports the coronary vasodilatory activity of2-n-pentyloxyadenosine, 2-(β-hydroxyethoxy)-adenosine, and2-phenoxyadenosine. However, there is no demonstration in U.S. Pat. No.3,936,439 or FR 2162128 that any of the compounds described could beadministered without causing serious side effects.

Ribeiro et al, (Progress in Neurobiology 68 (2003) 377-392) is a reviewof adenosine receptors in the nervous system. It is stated in theconcluding remarks of this article (on page 387, right column, lines4-10 of section 8) that “as noted a long time ago, activation ofadenosine receptors at the periphery is associated with hypotension,bradycardia and hypothermia [ . . . ] These side effects have so farsignificantly limited the clinical usefulness of adenosine receptoragonists”.

There is, therefore, a need to provide adenosine receptor agonists thatcan be administered with minimal side effects.

Certain aspects of the invention relate to the treatment of pain. Painhas two components, each involving activation of sensory neurons. Thefirst component is the early or immediate phase when a sensory neuron isstimulated, for instance as the result of heat or pressure on the skin.The second component is the consequence of an increased sensitivity ofthe sensory mechanisms innervating tissue which has been previouslydamaged. This second component is referred to as hyperalgesia, and isinvolved in all forms of chronic pain arising from tissue damage, butnot in the early or immediate phase of pain perception.

Thus, hyperalgesia is a condition of heightened pain perception causedby tissue damage. This condition is a natural response of the nervoussystem apparently designed to encourage protection of the damaged tissueby an injured individual, to give time for tissue repair to occur. Thereare two known underlying causes of this condition, an increase insensory neuron activity, and a change in neuronal processing ofnociceptive information which occurs in the spinal cord. Hyperalgesiacan be debilitating in conditions of chronic inflammation (e.g.rheumatoid arthritis), and when sensory nerve damage has occurred (i.e.neuropathic pain).

Two major classes of analgesics are known: (i) non steroidalanti-inflammatory drugs (NSAIDs) and the related COX-2 inhibitors; and(ii) opiates based on morphine. Analgesics of both classes are effectivein controlling normal, immediate or nociceptive pain. However, they areless effective against some types of hyperalgesic pain, such asneuropathic pain. Many medical practitioners are reluctant to prescribeopiates at the high doses required to affect neuropathic pain because ofthe side effects caused by administration of these compounds (such asrestlessness, nausea, and vomiting), and the possibility that patientsmay become addicted to them. NSAIDs are much less potent than opiates,so even higher doses of these compounds are required. However, this isundesirable because these compounds cause irritation of thegastro-intestinal tract.

There is also a need to provide analgesics, particularlyanti-hyperalgesics, which are sufficiently potent to control painperception in neuropathic and other hyperalgesic syndromes, and which donot have serious side effects or cause patients to become addicted tothem.

It has recently become apparent (WO 2004/052377; WO 2004/078183; WO2004/078184; WO 2005/084653) that some adenosine agonists (e.g.spongosine) are effective analgesics at doses as much as one hundredtimes lower than would be expected to be required based on the knownaffinity of this compound for adenosine receptors. At such doses,spongosine and related compounds do not cause the significant sideeffects associated with adenosine receptor activation. The underlyingmechanism behind these observations appears to be that these compoundshave increased affinity for adenosine receptors at pH below pH 7.4. Itis believed that this property explains the surprising activity of thesecompounds at low doses. The Applicant has been able to identify certainother compounds that also have increased affinity for adenosinereceptors at reduced pH. It is thought that these compounds can be usedas medicaments without causing serious side effects. However asignificant proportion of these compounds exhibit poor oralbioavailability and short plasma half lives, thus limiting theirusefulness as therapeutics.

Spongosine was first isolated from the tropical marine sponge,Cryptotethia crypta in 1945 (Bergmann and Feeney, J. Org. Chem. (1951)16, 981, Ibid (1956) 21, 226), and was the first methoxypurine found innature. It is also known as 2-methoxyadenosine, or 9H-purin-6-amine,9-α-D-arabinofuranosyl-2-methoxy. The first biological activities ofspongosine were described by Bartlett et al, (J. Med. Chem. (1981) 24,947-954). Spongosine (and other compounds) was tested for its skeletalmuscle-relaxant, hypothermic, cardiovascular and anti-inflammatoryeffects in rodents following oral administration (anti-inflammatoryactivity was assessed by inhibition of carageenan-induced oedema in arat paw). Spongosine caused 25% inhibition of carageenan-inducedinflammation in rats at 20 mg/kg po. However, reductions in mean bloodpressure (41%), and in heart rate (25%) were also observed afteradministration of this compound at this dose.

The affinity of spongosine for the rat adenosine A1 and A2A receptorshas been determined. The K_(d) values obtained (in the rat) were 340 nMfor the A1 receptor and 1.4 μM for the A2A receptor, while the EC₅₀value for stimulation of the rat A2A receptor was shown to be 3 μM (Dalyet al, Pharmacol. (1993) 46, 91-100). In the guinea pig, the efficacy ofspongosine was tested in the isolated heart preparation and the EC50values obtained were 10 μM and 0.7 μM for the adenosine A1 and A2Areceptors, respectively (Ueeda et al, J Med Chem (1991) 34, 1334-1339).Because of the low potency and poor receptor selectivity of thiscompound it was largely ignored in favor of more potent and receptorselective adenosine receptor agonists.

The use of nucleoside analogues in the treatment of diseases is oftenlimited by poor oral absorption (Han et al, Pharm. Res. (1998) 15(8),1154-9). Nucleosides are poorly soluble, polar molecules, and theseproperties make them poorly permeable to systemic membranes, such as theblood-brain barrier and the cellular membranes that provide access tothe drugs' targets (Kling, Modern Drug Discovery (1999) 2(3), 26-36).Thus, oral administration of nucleoside drugs often results in poor orirreproducible in vivo efficacy as a result of a limited or variableconcentration of the drug at the site of action. The design andsynthesis of new nucleoside analogues therefore remains a very activearea of research, with the goal of discovering drugs with optimal oralbioavailability (Dresser et al, Drug Metabolism and Disposition (2000)28, 9, 1135-40).

Numerous research groups have attempted to solve the problem of poororal bioavailability of nucleoside drugs by employing a pro-drug of thechosen bioactive species. A pro-drug is a drug which has been chemicallymodified and may be biologically inactive at its site of action, butwhich will be degraded or modified by one or more enzymatic or in vivoprocesses to the bioactive form.

The design of nucleoside pro-drugs has focused on improving oralbioavailabilty by the targeting of nucleoside or peptide transporters,through exploitation of enzymatic processes such adenosine deaminaseactivation, or by the appending of specific substituents to the sugarmoiety of the nucleoside, which aid membrane permeation and are thencleaved in vivo to release the active species.

Various pro-drugs of antivirals have been attempted. Most notably, U.S.Pat. No. 4,957,924 discloses various therapeutic esters of theantiherpetic agent, acyclovir. Valacyclovir, the L-valyl ester ofAcyclovir, is an oral prodrug that undergoes rapid and extensivefirst-pass metabolism to yield Acyclovir and the amino acid L-valine.The bioavailability of Acyclovir from oral Valacyclovir is considerablygreater than that achieved after oral Acyclovir administration. Oraladministration of Valacyclovir produced a greater increase in urinaryexcretion of Acyclovir (63%), compared with oral administration ofAcyclovir itself (19%) (Perry and Faulds Drugs (1996) 52, 754-72). Thisincrease in oral bioavailability has been attributed to interaction ofthe L-valyl ester moiety of Valacyclovir with the peptide transporterhPEPT1 (Sawada et al, J. Pharmacol. Exp. Ther. (1999) 291, 2, 705-9;Anand et al, J. Pharmacol. Exp. Ther. (2003) 304, 781). An analogousstrategy has been used to increase the oral bioavailability ofZidovudine (AZT) (Han et al, Pharm. Res. (1998) 15(8), 1154-9).

Similarly, WO 01/96353 relates to 3′-prodrugs of2′-deoxy-β-L-nucleosides for the treatment of hepatitis B virus, thatare amino acid esters including valyl and alkyl esters, specifically3′-L-amino acid ester and 3′,5′-L-diamino acid esters. For example, incynamalogous monkeys, the 3′,5′-divaline ester pro-drug of2′-deoxy-β-L-cytidine released 2′-deoxy-β-L-cytidine in vivo with 73%oral bioavailability and a 2.28 h (Po) half-life, in comparison to anoral bioavailability of 18% and a half-life of 2.95 h (po) followingdosing of 2′-deoxy-β-L-cytidine itself.

In an alternative approach, adenosine deaminase activation of pro-drugsto the active species has been exploited. For example, Viramidine hasbeen shown to act as a pro-drug to the chronic hepatitis C drug,Ribavarin. Viramidine is predominantly converted by adenosine deaminaseto Ribavarin in the liver and this liver-targeting property has beingexploited to circumvent haemolytic anaemia side effects caused byRibavarin itself. Thus, after multiple oral dosing of [¹⁴C]Ribavarin or[¹⁴C]Viramidine to monkey, Viramidine yielded three times the drug levelin the liver but only half in red blood cells compared to Ribavarin (Linet al, Antiviral chemistry & chemotherapy (2003) 14, 145-152; Wu et al,Journal of Antimicrobial Chemotherapy (2003) 52, 543-6).

WO 00/71558 discloses the use of pro-drugs that are esters of N6-oxa,thia, thioxa and azacycloalkyl substituted adenosine derivatives thatare selective adenosine A1 receptor agonists. Although an increase inobserved in vivo efficacy (fall in heart rate) was observed using thisstrategy, no data is presented proving this to be a result of anyincrease in oral bioavailability or effective half-life. Sommadossi etal. (WO 2004/003000) have disclosed 2′ and 3′-pro-drugs of 1′, 2′, 3′ or4′, SS-D or SS-L, branched nucleosides for treating flaviviridaeinfections but similarly have not demonstrated that these pro-drugsimprove oral bioavailabilty or half-life. Dalpiaz et al (ActaTechnologiae et Legis Medicamenti (2002) 13, 49 and Pharm. Res. (2001)18, 531) have reported stability data of 5′-ester pro-drugs of6-cyclopentylaminoadenosine (CPA) in whole blood and plasma.

DISCLOSURE OF THE INVENTION

The present invention provides the use in therapy of novel 2′-methoxypro-drugs of adenosine derivatives that are converted within themammalian body to become therapeutically useful adenosine receptoragonists or antagonists. The 2′-methoxy functionality, despite beingonly a small structural modification to the nucleoside template, cansurprisingly cause a significant increase in both the oralbioavailability and oral half-life of the pro-drugged adenosinederivative (active metabolite) reaching the receptor target, incomparison to the oral bioavailability and oral half-life that isobserved following oral dosing of the metabolite itself (i.e. when thispro-drug strategy is not employed).

In a first preferred aspect, the invention provides the use of acompound of Formula I, or a pharmaceutically acceptable salt thereof,

wherein:

R1 is adenine, which is unsubstituted or substituted with 1-3substituents independently selected from halogen, OH, OR4, NR4R5, CN,SR4 or R4;

R2 is selected from CH₂OH, CH₂OR4, CH₂R4, R4, CH₂CO2R4, CH₂CONR4R5,CH₂NR4R5, CH₂halogen, CO₂R4, CONR4R5, CH₂OCOR4, CH₂OCONR4R5, CH₂NHCOR4or CH₂NHCONR4R5;

R3 is selected from F, OH, OR4, NH₂, N₃ or NR4R5;

R4 and R5 are independently selected from H, C₁₋₆-alkyl,C₃₋₈-cycloalkyl, aryl or heterocyclyl, each optionally substituted with1-3 substituents independently selected from halogen, OH, NH₂, CN orCF₃;

in the manufacture of a medicament for use against a medical conditionthat can be improved or prevented by agonism or antagonism of anadenosine receptor.

Preferably, the said compound of Formula I is having the formula II, ora pharmaceutically acceptable salt thereof,

wherein R1 is as described for Formula I.

In a preferred aspect of the invention, the said medical condition canbe improved or prevented by agonism of an adenosine receptor. Inparticular, the said medical condition can be associated with pain,inflammation and/or arthropathy.

In a further aspect, the invention provides the use of a compound ofFormula (I) or (II) in the manufacture of an improved medicament havingincreased bioavailability and/or half-life in comparison with a secondmedicament, said second medicament having as active ingredient acompound of Formula IV, or a pharmaceutically acceptable salt thereof,

wherein R1 is as defined for Formula I, and wherein R1 of the secondmedicament is the same as R1 of the improved medicament.

In another aspect, the invention provides a method of preventing,treating, or ameliorating a medical condition that can be prevented orimproved by agonism or antagonism of an adenosine receptor, whichcomprises administering a compound of the Formula I or II, wherein R1,R2 and R3 are as defined above, to a subject in need of such prevention,treatment, or amelioration. In a preferred aspect of the invention, thesaid medical condition can be improved or prevented by agonism of anadenosine receptor. In particular, the said medical condition can beassociated with pain, inflammation and/or arthropathy.

Methods delineated herein include those wherein the subject isidentified as in need of a particular stated treatment. Identifying asubject in need of such treatment can be in the judgment of a subject ora health care professional and can be subjective (e.g. opinion) orobjective (e.g. measurable by a test or diagnostic method).

In yet another aspect, the invention provides a method for increasingbioavailability and/or half-life of a compound having the Formula IV, ora pharmaceutically acceptable salt thereof,

wherein R1 is as defined for Formula I, said method comprisingsubstituting 2′-OH in the ribose moiety to 2′-OMe.

In another aspect, the invention provides a compound having the FormulaIII, or a pharmaceutically acceptable salt thereof,

wherein R6 is selected from OR4, NR4R5, CN, SR4 or R4; wherein R4 and R5are as defined for Formula I; with the proviso that NR4R5 is not NH₂,NHphenyl or NHpentyl; and with the proviso that R4 is not methyl,propyl, isopropyl, phenyl or C≡CCH₂OH.

R6 can preferably be OMe, OCH₂CHF₂, OCH₂cyclopentyl,O(2,2,3,3-tetrafluorocyclobutyl), (2,5-difluorophenoxy),(3,4-difluorophenoxy), (3-trifluoromethyl, 4-chlorophenoxy),(S)-sec-butylamino, or cyclohexylamino.

Preferred compounds of Formula III include:

-   -   (2R,3R,4R,5R)-5-(6-amino-2-methoxy-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-[6-amino-2-(2,2-difluoroethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-[6-amino-2-(cyclopentylmethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-{6-amino-2-[(2,2,3,3-tetrafluorocyclobutyl)oxy]-9H-purin-9-yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-[6-amino-2-(2,5-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-[6-amino-2-(3,4-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-[6-amino-2-[4-chloro-3-(trifluoromethyl)phenoxy]-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;    -   (2R,3R,4R,5R)-5-(6-amino-2-{[(1S)-1-methylpropyl]amino}-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;        and    -   (2R,3R,4R,5R)-5-[6-amino-2-(cyclohexylamino)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;        or a pharmaceutically acceptable salt thereof.

There are also provided according to the invention methods of synthesisof compound numbers 1-9 as set out in the examples below. In some casesthe precursors of these compounds include one or more protecting groups.It will be appreciated that, if desired, other carboxy-based hydroxylprotecting groups may be used instead of those specified. Other aspectsinclude:

-   -   A process for producing        (2R,3R,4R,5R)-5-(6-amino-2-methoxy-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with NaOMe and MeOH.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-(2,2-difluoroethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ROH and de-protecting the reaction product, wherein R is        CH₂CHF₂.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-(cyclopentylmethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ROH and de-protecting the reaction product, wherein R is        CH₂cyclopentyl.    -   A process for producing        (2R,3R,4R,5R)-5-{6-amino-2-[(2,2,3,3-tetra-fluorocyclobutyl)oxy]-9H-purin-9-yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ROH and de-protecting the reaction product, wherein R is        2,2,3,3-tetrafluorocyclobutyl.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-(2,5-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ArOH, and de-protecting the reaction product, wherein Ar is        2,5-difluorophenyl.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-(3,4-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ArOH, and de-protecting the reaction product, wherein Ar is        3,4-difluorophenyl.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-[4-chloro-3-(trifluoromethyl)phenoxy]-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with ArOH, and de-protecting the reaction product, wherein Ar is        3-(trifluoromethyl)-4-chlorophenyl.    -   A process for producing        (2R,3R,4R,5R)-5-(6-amino-2-{[(1S)-1-methylpropyl]amino}-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with RR′NH and de-protecting the reaction product, wherein RR′N        is NH—(S)-sec-butyl.    -   A process for producing        (2R,3R,4R,5R)-5-[6-amino-2-(cyclohexylamino)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol,        comprising reacting tetrabenzoyl-2′-methoxy-2-nitro-adenosine        with RR′NH and de-protecting the reaction product, wherein RR′N        is NHcyclohexyl.

Prodrugs of the invention are all believed to give rise, in vivo, toactive metabolites that have increased affinity for adenosine receptorsat pH below pH 7.4. In normal mammalian tissues extracellular pH istightly regulated between pH 7.35 and 7.45. Some tissues experiencelower pH values, particularly the lumen of the stomach (pH between 2 and3) and the surfaces of some epithelia (for example, the lung surface pHis approximately 6.8). In pathological tissues, for example duringinflammation, ischaemia and other types of damage, a reduction in pHoccurs.

Because of the increased affinity of the active metabolites (resultingin vivo from the pro-drugs of the invention) for adenosine receptors atreduced pH, it is thought that the actions of these active metabolitescan be targeted to regions of low pH, such as pathological tissues.Consequently, the doses of these active metabolites that are required togive therapeutic effects are much lower than would be expected based ontheir affinity for adenosine receptors at normal extracellularphysiological pH. Since only low doses of the active metabolites arerequired, the serious side effects associated with administration ofadenosine receptor agonists, which render them unusable as therapeuticagents, are avoided or minimized.

As described above, the disclosed prodrug compounds can be used for theprevention, treatment, or amelioration of pathological conditions thatcan be improved or prevented by modulation (agonism or antagonism) ofadenosine receptors, such as adenosine A2A receptors. Examples of suchpathological conditions include pain, inflammation and/or arthropathy.

According to the invention there is provided use of a pro-drug of theinvention in the manufacture of a medicament for the prevention,treatment, or amelioration of pain, particularly hyperalgesia. There isalso provided according to the invention a method of preventing,treating, or ameliorating pain (particularly hyperalgesia) whichcomprises administering a pro-drug of the invention to a subject in needof such prevention, treatment, or amelioration.

Pro-drugs of the invention are believed to give rise in vivo, to activemetabolites that are effective in inhibiting pain perception in mammalssuffering from pain, in particular neuropathic or inflammatory pain,even when the pro-drugs are administered at doses expected to giveplasma concentrations of the active metabolites well below those knownto activate adenosine receptors. Therefore, it is believed thatpro-drugs of the invention can treat pain (particularly neuropathic andinflammatory pain) without causing the significant side effectsassociated with administration of other adenosine receptor agonists.

As mentioned above hyperalgesia is a consequence in most instances oftissue damage, either damage directly to a sensory nerve, or damage ofthe tissue innervated by a given sensory nerve. Consequently, there aremany conditions in which pain perception includes a component ofhyperalgesia.

According to the invention there is provided use of a pro-drug of theinvention as an analgesic (particularly an anti-hyperalgesic) for theprevention, treatment, or amelioration of pain (particularlyhyperalgesia) caused as a result of neuropathy, including DiabeticNeuropathy, Polyneuropathy, Cancer Pain, Fibromyalgia, Myofascial PainSyndrome, Osteoarthritis, Pancreatic Pain, Pelvic/Perineal pain, PostHerpetic Neuralgia, Rheumatoid Arthritis, Sciatica/Lumbar Radiculopathy,Spinal Stenosis, Temporo-mandibular Joint Disorder, HIV pain, TrigeminalNeuralgia, Chronic Neuropathic Pain, Lower Back Pain, Failed BackSurgery pain, back pain, post-operative pain, post physical trauma pain(including gunshot, road traffic accident, burns), Cardiac pain, Chestpain, Pelvic pain/PID, Joint pain (tendonitis, bursitis, acutearthritis), Neck Pain, Bowel Pain, Phantom Limb Pain, Obstetric Pain(labour/C-Section), Renal Colic, Acute Herpes Zoster Pain, AcutePancreatitis Breakthrough Pain (Cancer), Dysmenorhoea/Endometriosis; orin any of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition.

According to the invention there is also provided use of a pro-drug ofthe invention as an analgesic (particularly an anti-hyperalgesic) forthe prevention, treatment, or amelioration of pain (particularlyhyperalgesia) caused as a result of inflammatory disease, or as a resultof combined inflammatory, autoimmune and neuropathic tissue damage,including rheumatoid arthritis, osteoarthritis, rheumatoid spondylitis,gouty arthritis, and other arthritic conditions, cancer, HIV, ChronicObstructive Pulmonary Disease (COPD), acute bronchitis, chronicbronchitis, emphysema, bronchiectasis, cystic fibrosis, pneumonia,pleurisy, acute asthma, chronic asthma, acute respiratory distresssyndrome, adult respiratory distress syndrome (ARDS), infant respiratorydistress syndrome (IRDS) acute lung injury (ALI), laryngitis,pharangitis, persistent asthma, chronic asthmatic bronchitis,interstitial lung disease, lung malignancies, alpha-anti-trypsindeficiency, bronchiolitis obliterans, sarcoidosis, pulmonary fibrosis,collagen vascular disorders, allergic rhinitis, nasal congestion, statusasthmaticus, smoking related pulmonary disease, pulmonary hypertension,pulmonary oedema, pulmonary embolism, pleural effusion, pneumothorax,haemothorax, lung cancer, allergies, pollinosis Hay fever), sneeze,vasomotor rhinitis, mucositis, sinusitis, exogenous irritant inducedillness (SO₂, smog, pollution), airway hypersensitivity, milk productintolerance, Luffer's pneumonia, pneumoconiosis, collagen inducedvascular disease, granulomatous disease, bronchial inflammation, chronicpulmonary inflammatory disease, bone resorption diseases, reperfusioninjury (including damage caused to organs as a consequence ofreperfusion following ischaemic episodes e.g. myocardial infarcts,strokes), autoimmune damage (including multiple sclerosis, Guillam BarreSyndrome, myasthenia gravis) graft v. host rejection, allograftrejections, fever and myalgia due to infection, AIDS related complex(ARC), keloid formation, scar tissue formation, Crohn's disease,ulcerative colitis and pyresis, irritable bowel syndrome, osteoporosis,cerebral malaria and bacterial meningitis, bowel pain, cancer pain, backpain, fibromyalgia, post-operative pain; or in any of the abovepathological conditions where bacterial or viral infection is a cause orexacerbates the condition.

It is believed that pro-drugs of the invention may give rise, in vivo,to active metabolites that are effective in the prevention, treatment,or amelioration of ischaemic pain. The term “ischaemic pain” is usedherein to mean pain associated with a reduction in blood supply to apart of the body. A reduced blood supply limits the supply of oxygen(hypoxia) and energy to that part of the body. Ischaemia arises frompoor blood perfusion of tissues and so ischaemic pain arises in coronaryartery disease, peripheral artery disease, and conditions which arecharacterized by insufficient blood flow, usually secondary toatherosclerosis. Other vascular disorders can also result in ischaemicpain. These include: left ventricular hypertrophy, coronary arterydisease, essential hypertension, acute hypertensive emergency,cardiomyopathy, heart insufficiency, exercise tolerance, chronic heartfailure, arrhythmia, cardiac dysrhythmia, syncopy, arteriosclerosis,mild chronic heart failure, angina pectoris, Prinzmetal's (variant)angina, stable angina, and exercise induced angina, cardiac bypassreocclusion, intermittent claudication (arteriosclerosis oblitterens),arteritis, diastolic dysfunction and systolic dysfunction,atherosclerosis, post ischaemia/reperfusion injury, diabetes (both TypesI and II), thromboembolisms. Haemorrhagic accidents can also result inischaemic pain. In addition poor perfusion can result in neuropathic andinflammatory pain arising from hypoxia-induced nerve cell damage (e.g.in cardiac arrest or bypass operation, diabetes or neonatal distress);or in any of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition.

Pro-drugs of the invention are believed to give rise, in vivo, to activemetabolites that are effective in prevention, treatment, or ameliorationof ischaemic pain even when the pro-drugs are administered at dosesexpected to give plasma concentrations of the active metabolites wellbelow those known to activate adenosine receptors. At these doses, it isbelieved that the active metabolites do not cause the significant sideeffects associated with administration of higher doses of adenosinereceptor agonists.

There is further provided according to the invention use of a pro-drugof the invention (i.e. a compound of the invention) for the manufactureof a medicament for the prevention, treatment, or amelioration ofinflammation. There is further provided according to the invention amethod of prevention, treatment, or amelioration of inflammation, whichcomprises administering a pro-drug of the invention to a subject in needof such prevention, treatment, or amelioration.

In particular, it is believed that pro-drugs of the invention (i.e.compounds of the invention) can be used to prevent, treat, or ameliorateinflammation caused by or associated with: cancer (such as leukemias,lymphomas, carcinomas, colon cancer, breast cancer, lung cancer,pancreatic cancer, hepatocellular carcinoma, kidney cancer, melanoma,hepatic, lung, breast, and prostate metastases, etc.); auto-immunedisease (such as organ transplant rejection, lupus erythematosus, graftv. host rejection, allograft rejections, multiple sclerosis, rheumatoidarthritis, type I diabetes mellitus including the destruction ofpancreatic islets leading to diabetes and the inflammatory consequencesof diabetes); autoimmune damage (including multiple sclerosis, GuillamBarre Syndrome, myasthenia gravis); obesity; cardiovascular conditionsassociated with poor tissue perfusion and inflammation (such asatheromas, atherosclerosis, stroke, ischaemia-reperfusion injury,claudication, spinal cord injury, congestive heart failure, vasculitis,haemorrhagic shock, vasospasm following subarachnoid haemorrhage,vasospasm following cerebrovascular accident, pleuritis, pericarditis,the cardiovascular complications of diabetes); ischaemia-reperfusioninjury, ischaemia and associated inflammation, restenosis followingangioplasty and inflammatory aneurysms; epilepsy, neurodegeneration(including Alzheimer's Disease), muscle fatigue or muscle cramp(particularly athletes' cramp), arthritis (such as rheumatoid arthritis,osteoarthritis, rheumatoid spondylitis, gouty arthritis), fibrosis (forexample of the lung, skin and liver), multiple sclerosis, sepsis, septicshock, encephalitis, infectious arthritis, Jarisch-Herxheimer reaction,shingles, toxic shock, cerebral malaria, Lyme's disease, endotoxicshock, gram negative shock, haemorrhagic shock, hepatitis (arising bothfrom tissue damage or viral infection), deep vein thrombosis, gout;conditions associated with breathing difficulties (e.g. impeded andobstructed airways, bronchoconstriction, pulmonary vasoconstriction,impeded respiration, silicosis, pulmonary sarcosis, pulmonaryhypertension, pulmonary vasoconstriction, bronchial allergy and vernalconjunctivitis); conditions associated with inflammation of the skin(including psoriasis, eczema, ulcers, contact dermatitis); conditionsassociated with inflammation of the bowel (including Crohn's disease,ulcerative colitis and pyresis, irritable bowel syndrome, inflammatorybowel disease); HIV (particularly HIV infection), cerebral malaria,bacterial meningitis, TNF-enhanced HIV replication, TNF inhibition ofAZT and DDI activity, osteoporosis and other bone resorption diseases,osteoarthritis, rheumatoid arthritis, infertility from endometriosis,fever and myalgia due to infection, cachexia secondary to cancer,cachexia secondary to infection or malignancy, cachexia secondary toacquired immune deficiency syndrome (AIDS), AIDS related complex (ARC),keloid formation, scar tissue formation, adverse effects fromamphotericin B treatment, adverse effects from interleukin-2 treatment,adverse effects from OKT3 treatment, or adverse effects from GM-CSFtreatment, and other conditions mediated by excessive anti-inflammatorycell (including neutrophil, eosinophil, macrophage and T-cell) activity;or in any of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition.

Continuous low grade inflammation is known to be associated with obesity(in the presence and absence of insulin resistance and Type II diabetes)(Browning et al Metabolism (2004) 53, 899-903, Inflammatory markerselevated in blood of obese women; Mangge et al, Exp Clin EndocrinolDiabetes (2004) 112, 378-382, Juvenile obesity correlates with seruminflammatory marker C-reactive protein; Maachi et al Int J Obes RelatMetab Disord. (2004) 28, 993-997, Systemic low grade inflammation inobese people). A possible reason for this is that fat cells secrete TNFalpha and interleukins 1 and 6, which are pro-inflammatory.

Pro-drugs of the invention that give rise, in vivo, to activemetabolites that are selective agonists of adenosine A2A and/or A3receptors are particularly preferred because it is believed that suchmetabolites will have strong anti-inflammatory activity. By selectiveagonists of adenosine A2A and/or A3 receptors is meant agonists thatactivate adenosine A2A and/or A3 receptors at concentrations that arelower (preferably one thousandth to one fifth) than required to activateadenosine A1 receptors. Furthermore, A1 receptors have pro-inflammatoryactivity, so such effects are expected to be minimized for compoundsthat are selective for A2A and/or A3 receptors.

It will be appreciated that any pathological condition that can beprevented or improved by agonism of adenosine A2A and/or A3 receptorscan be prevented, treated, or ameliorated by pro-drugs of the invention.

According to the invention there is provided use of a pro-drug of theinvention in the manufacture of a medicament for the prevention,treatment, or amelioration of a pathological condition that can beimproved or prevented by agonism of adenosine A2A and/or A3 receptors.There is also provided according to the invention a method ofprevention, treatment, or amelioration of a pathological condition thatcan be improved or prevented by agonism of adenosine A2A and/or A3receptors, which comprises administering a pro-drug of the invention toa subject in need of such prevention, treatment, or amelioration.

A person of ordinary skill in the art can readily test whether or not apathological condition that is prevented, treated, or ameliorated by acompound of the invention is acting via adenosine A2A and/or A3receptors. For example, this may be done by comparing the effect of thecompound in an animal model of the pathological condition in thepresence and absence of a selective antagonist of an adenosine A2Aand/or A3 receptor. If the effect of the compound in the presence of theantagonist is reduced or absent compared with the effect of the compoundin the absence of the antagonist, it is concluded that the compound isexerting its effect via an adenosine A2A and/or A3 receptor. Antagonistsof adenosine A2A and A3 receptors are known to those of ordinary skillin the art (see for example Ongini et al., Farmaco. (2001)January-February, 56(1-2), 87-90; Muller, Curr Top Med Chem. (2003)3(4), 445-62).

Alternatively, an adenosine A2A receptor knockout mouse may be used(Ohta A and Sitkovsky M, Nature (2001) 414, 916-20). For example, theeffect of the compound on a mouse that has symptoms of the pathologicalcondition is compared with its effect on an adenosine A2A knockout mousethat has corresponding symptoms. If the compound is only effective inthe mouse that has adenosine A2A receptors it is concluded that thecompound is exerting its effect via adenosine A2A receptors.

Pro-drugs of the invention are believed give rise, in vivo, to activemetabolites that are much more effective at low doses than otheradenosine receptor agonists. Thus, it is expected that pro-drugs of theinvention can be effectively administered at doses at which they havereduced probability and severity of side effects, or at which sideeffects are not observed. Such compounds provide significant advantagesover the vast majority of other adenosine receptor agonists which onlyhave anti-inflammatory effects at the same concentrations at whichserious side effects are observed.

Compounds of the invention may alternatively or additionally havereduced probability and severity of side effects compared to otheradenosine receptor agonists.

It is also believed that pro-drugs of the invention may be effective asdisease-modifying anti-rheumatic drugs (DMARDs), in particular for usein the prevention, treatment, or amelioration of rheumatoid arthritis,and possibly other arthropathies such as osteoarthritis.

Medications used to treat rheumatoid arthritis (RA) can be divided intotwo groups: those that help relieve RA symptoms; and those that helpmodify the disease. Drugs that help to relieve RA symptoms includenonsteroidal anti-inflammatory drugs (NSAIDs) that relieve pain andreduce inflammation in the affected joints, analgesics (such asacetaminophen and narcotic pain medications) that relieve pain but donot slow joint damage or reduce inflammation, and corticosteroids thatare anti-inflammatory drugs.

DMARDs help to improve RA symptoms (such as joint swelling andtenderness), but also slow the progression of joint damage caused by RA.Thus, while there is no cure for RA, DMARDs help to slow the progressionof RA. In the past DMARDs were usually used to treat RA after NSAIDtherapy failed. However, DMARDs are now beginning to be used earlier inthe course of RA because studies have suggested that early interventionwith DMARDs offers important benefits. DMARDs and NSAIDs are often usedin combination with each other.

Results from clinical studies have shown that known DMARDs slow theprogression of RA. After 6 months of treatment, the rate of bone andcartilage damage had already started to slow in patients' joints. After1 year, patients showed very little progression of joint damage, andafter 2 years X rays showed that few patients in the study had newlydamaged joints during the second year of treatment.

Examples of known DMARDs include sulphasalazine, penicillamine,chloroquine, hydroxychloroquine, gold (by intranuscular injection ororally as auranofin), methotrexate, cyclosporin, azathioprine,cyclophosphamide, leflunomide. More recently biological DMARDs have beendeveloped which inhibit tumour necrosis factor alpha (TNF alpha). Oneexample is Humira® which is indicated for reducing signs and symptomsand inhibiting the progression of structural damage in adults withmoderately to severely active RA who have had an inadequate response toone or more DMARDs. Humira® is an anti-TNF alpha antibody.

Many of the known DMARDs cause serious side effects. Consequently, it isdesired to provide new DMARDs that can be administered with minimal sideeffects.

WO 2005/084653 shows the ability of spongosine to reduce phorbol esterinduced TNF alpha release in U937 human macrophage cells. On this basis,it is believed that spongosine and related compounds of the inventionalso have DMARD activity.

According to the invention there is provided use of a pro-drug of theinvention in the manufacture of a medicament for slowing the progressionof arthropathy. There is also provided according to the invention amethod of slowing the progression of arthropathy, which comprisesadministering a pro-drug of the invention to a subject in need thereof.

Preferably the progression of RA is slowed, and in particular theprogression of joint damage caused by RA. A compound of the inventionmay be administered to the subject at any stage in the course of RA. Acompound of the invention may be administered in combination with one ormore NSAIDs or other DMARDs.

Pro-drugs of the invention are believed to give rise, in vivo, to activemetabolites that are effective as DMARDs even when the pro-drugs areadministered at doses expected to give plasma concentrations of theactive metabolites well below those known to activate adenosinereceptors. At these doses, it is believed that the active metabolites donot cause the significant side effects associated with administration ofhigher doses of spongosine, or other adenosine receptor agonists.

A particular advantage of use of pro-drugs of the invention as DMARDs isthat it is believed that they will be orally active, in contrast toanti-TNF alpha antibodies which must be injected.

It has also been appreciated that pro-drugs of the invention may giverise, in vivo, to active metabolites that may be effective inpreventing, treating, or ameliorating macro and micro vascularcomplications of type 1 or 2 diabetes (including retinopathy,nephropathy, autonomic neuropathy), or blood vessel damage caused byischaemia (either diabetic or otherwise) or atherosclerosis (eitherdiabetic or otherwise).

According to the invention, there is provided use of a pro-drug of theinvention in the manufacture of a medicament for the prevention,treatment, or amelioration of macro or micro vascular complications oftype 1 or 2 diabetes, retinopathy, nephropathy, autonomic neuropathy, orblood vessel damage caused by ischaemia or atherosclerosis. According tothe invention there is also provided a method of preventing, treating,or ameliorating macro or micro vascular complications of type 1 or 2diabetes, retinopathy, nephropathy, autonomic neuropathy, or bloodvessel damage caused by ischaemia or atherosclerosis, in a subject inneed of such prevention, treatment, or amelioration, which comprisesadministering a pro-drug of the invention to the subject.

Pro-drugs of the invention are believed to be effective in prevention,treatment, or amelioration of macro or micro vascular complications oftype 1 and 2 diabetes, including retinopathy, nephropathy, autonomicneuropathy, or blood vessel damage caused by ischaemia oratherosclerosis (either diabetic or otherwise)) even when the pro-drugsare administered at doses expected to give plasma concentrations of theactive metabolites resulting in vivo, well below those known to activateadenosine receptors. At these doses, it is believed that the compoundsdo not cause the significant side effects associated with administrationof higher doses of adenosine receptor agonists.

Pro-drugs of the invention are also believed to be effective in thepromotion of wound healing. According to the invention there is provideduse of a pro-drug of the invention in the manufacture of a medicamentfor the promotion of wound healing. There is also provided according tothe invention a method of promoting wound healing in a subject, whichcomprises administering a pro-drug of the invention to the subject.

The amount of a pro-drug of the invention that is administered to asubject is preferably an amount which gives rise to a peak plasmaconcentration of the active metabolite resulting in vivo, that is lessthan the EC₅₀ value of the compound at adenosine receptors (preferablyat pH 7.4).

It will be appreciated that the EC₅₀ value of the active metabolite islikely to be different for different adenosine receptors (i.e. the A1,A2A, A2B, A3 adenosine receptors). The amount of the pro-drug that is tobe administered should be calculated relative to the lowest EC₅₀ valueof the active metabolite at the different receptors.

Thus, preferably the amount of a pro-drug of the invention that isadministered to a subject should be an amount which gives rise to a peakplasma concentration of the active metabolite resulting in vivo, that isless than the lowest EC₅₀ value of the active metabolite at adenosinereceptors.

Preferably the peak plasma concentration of the active metaboliteresulting in vivo following dosing of the pro-drug, is one tenthousandth to one half (or one ten thousandth to one fifth, or one tenthousandth to one twentieth, or one ten thousandth to one hundredth, orone ten thousandth to one thousandth, or one thousandth to one half, orone thousandth to one fifth, or one thousandth to one twentieth, or onefiftieth to one tenth, or one hundredth to one half, or one hundredth toone fifth, or one fiftieth to one third, or one fiftieth to one half, orone fiftieth to one fifth, or one tenth to one half, or one tenth to onefifth) of the lowest EC₅₀ value.

Preferably the amount of a pro-drug of the invention that isadministered gives rise to a plasma concentration of the activemetabolite resulting in vivo, that is maintained for more than one hourat one ten thousandth to one half (or one ten thousandth to one fifth,or one ten thousandth to one twentieth, or one ten thousandth to onehundredth, or one ten thousandth to one thousandth, or one thousandth toone half, or one thousandth to one fifth, or one thousandth to onetwentieth, or one fiftieth to one tenth, or one hundredth to one half,or one hundredth to one fifth, or one fiftieth to one half, or onefiftieth to one fifth, or one tenth to one half, or one tenth to onefifth) of the lowest EC₅₀ value of the active metabolite at adenosinereceptors.

Preferably the amount of the pro-drug administered gives rise to aplasma concentration of the active metabolite resulting in vivo that ismaintained for more than one hour between one thousandth and one half,or one thousandth and one fifth, or one thousandth and one twentieth, orone hundredth and one half, or one hundredth and one fifth, or onefiftieth and one half, or one fiftieth and one fifth, of the EC₅₀ valueof the active metabolite at adenosine receptors at pH 7.4.

For the avoidance of doubt, the EC₅₀ value of a compound is definedherein as the concentration of the compound that provokes a receptorresponse halfway between the baseline receptor response and the maximumreceptor response (as determined, for example, using a dose-responsecurve).

The EC₅₀ value should be determined under standard conditions (balancedsalt solutions buffered to pH 7.4). For EC₅₀ determinations usingisolated membranes, cells and tissues this would be in buffered saltsolution at pH 7.4 (e.g. cell culture medium), for example as in Daly etal., Pharmacol. (1993) 46, 91-100), or preferably as in Tilburg et al(J. Med. Chem. (2002) 45, 91-100). The EC₅₀ could also be determined invivo by measuring adenosine receptor mediated responses in a normalhealthy animal, or even in a tissue perfused under normal conditions(i.e. oxygenated blood, or oxygenated isotonic media, also buffered atpH 7.4) in a normal healthy animal.

Alternatively, the amount of a pro-drug of the invention that isadministered may be an amount that results in a peak plasmaconcentration of the active metabolite resulting in vivo, that is lessthan the lowest or highest K_(d) value of the compound at adenosinereceptors (i.e. less than the lowest or highest K_(d) value of thecompound at A1, A2A, A2B, and A3 adenosine receptors). Preferably thepeak plasma concentration of the active metabolite, is one tenthousandth to one half (or one ten thousandth to one fifth, or one tenthousandth to one twentieth, or one ten thousandth to one hundredth, orone ten thousandth to one thousandth, or one thousandth to one half, orone thousandth to one third, or one thousandth to one fifth, or onethousandth to one twentieth, or one fiftieth to one tenth, or onehundredth to one half, or one hundredth to one fifth, or one fiftieth toone half, or one fiftieth to one fifth, or one tenth to one half, or onetenth to one fifth) of the lowest or highest K_(d) value.

Preferably the amount of the pro-drug that is administered is an amountthat results in a plasma concentration of the active metaboliteresulting in vivo, that is maintained for at least one hour between onethousandth and one half, or one thousandth and one fifth, morepreferably between one thousandth and one twentieth, or one hundredthand one half, or one hundredth and one fifth, or one fiftieth and onehalf, or one fiftieth and one fifth, of the K_(d) value of the activemetabolite at adenosine receptors.

Preferably the amount of the pro-drug that is administered is an amountthat results in a plasma concentration of the active metaboliteresulting in vivo, that is maintained for more than one hour at one tenthousandth to one half (or one ten thousandth to one fifth, or one tenthousandth to one twentieth, or one ten thousandth to one hundredth, orone ten thousandth to one thousandth, or one thousandth to one half, orone thousandth to one fifth, or one thousandth to one twentieth, or onefiftieth to one tenth, or one hundredth to one half, or one hundredth toone fifth, or one fiftieth to one half, or one fiftieth to one fifth, orone fiftieth to one third, or one tenth to one half, or one tenth to onefifth) of the lowest or highest K_(d) value of the active metabolite atadenosine receptors.

The K_(d) value of the active metabolite, resulting in vivo followingadministration of the pro-drug, at each receptor should be determinedunder standard conditions using plasma membranes as a source of theadenosine receptors derived either from tissues or cells endogenouslyexpressing these receptors or from cells transfected with DNA vectorsencoding the adenosine receptor genes. Alternatively whole cellpreparations using cells expressing adenosine receptors can be used.Labeled ligands (e.g. radiolabeled) selective for the differentreceptors should be used in buffered (pH 7.4) salt solutions (see e.g.Tilburg et al, J. Med. Chem. (2002) 45, 420-429) to determine thebinding affinity and thus the K_(d) of the active metabolite at eachreceptor.

Alternatively, the amount of a pro-drug of the invention that isadministered may be an amount that is one ten thousandth to one half (orone ten thousandth to one fifth, or one ten thousandth to one twentieth,or one ten thousandth to one hundredth, or one ten thousandth to onethousandth, or one thousandth to one half, or one thousandth to onefifth, or one thousandth to one twentieth, or one fiftieth to one tenth,or one hundredth to one half, or one hundredth to one fifth, or onefiftieth to one half, or one fiftieth to one third, or one fiftieth toone fifth, or one tenth to one half, or one tenth to one fifth) of theminimum amount (or dose) of the pro-drug that gives rise to bradycardia,hypotension or tachycardia side effects in animals of the same speciesas the subject to which the compound is to be administered. Preferablythe amount of the pro-drug administered gives rise to a plasmaconcentration of the active metabolite resulting in vivo, that ismaintained for more than one hour at one ten thousandth to one half (orone ten thousandth to one fifth, or one ten thousandth to one twentieth,or one ten thousandth to one hundredth, or one ten thousandth to onethousandth, or one thousandth to one half, or one thousandth to onefifth, or one thousandth to one twentieth, or one fiftieth to one tenth,or one hundredth to one half, or one hundredth to one fifth, or onefiftieth to one half, or one fiftieth to one fifth, or one tenth to onehalf, or one tenth to one fifth) of the minimum amount of the activemetabolite that gives rise to the side effects.

Preferably the amount of the pro-drug administered gives rise to aplasma concentration of the active metabolite resulting in vivo, that ismaintained for more than 1 hour between one thousandth and one half, orone thousandth and one twentieth, or one hundredth or one fiftieth andone half, or one hundredth or one fiftieth and one fifth of the minimumdose that gives rise to the side effects.

Alternatively, the amount of a pro-drug of the invention that isadministered may be an amount that gives rise to a plasma concentrationof the active metabolite resulting in vivo, that is one ten thousandthto one half (or one ten thousandth to one fifth, or one ten thousandthto one twentieth, or one ten thousandth to one hundredth, or one tenthousandth to one thousandth, or one thousandth to one half, or onethousandth to one fifth, or one thousandth to one twentieth, or onefiftieth to one tenth, or one hundredth to one half, or one hundredth toone fifth, or one fiftieth to one half, or one fiftieth to one third, orone fiftieth to one fifth, or one tenth to one half, or one tenth to onefifth) of the minimum plasma concentration of the active metabolite thatcauses bradycardia, hypotension or tachycardia side effects in animalsof the same species as the subject to which the compound is to beadministered. Preferably the amount of the pro-drug administered givesrise to a plasma concentration of the active metabolite, that ismaintained for more than one hour at one ten thousandth to one half (orone ten thousandth to one fifth, or one ten thousandth to one twentieth,or one ten thousandth to one hundredth, or one ten thousandth to onethousandth, or one thousandth to one half, or one thousandth to onefifth, or one thousandth to one twentieth, or one fiftieth to one tenth,or one hundredth to one half, or one hundredth to one fifth, or onefiftieth to one half, or one fiftieth to one fifth, or one tenth to onehalf, or one tenth to one fifth) of the minimum plasma concentration ofthe active metabolite that causes the side effects.

Preferably the amount of the pro-drug administered gives rise to aplasma concentration of the active metabolite resulting in vivo, that ismaintained for more than 1 hour between one thousandth and one half, orone thousandth and one twentieth, or one hundredth or one fiftieth andone half, or one hundredth or one fiftieth and one fifth, of the minimumplasma concentration that causes the side effects.

The appropriate dosage of a pro-drug of the invention will vary with theage, sex, weight, and condition of the subject being treated, thepotency of the pro-drug and/or the active metabolite resulting in vivofollowing dosing of the pro-drug, (such as their EC₅₀ values for anadenosine receptor), the half life of the pro-drug and/or the activemetabolite, its absorption by the body, and the route of administration,etc. However, the appropriate dosage can readily be determined by oneskilled in the art.

A suitable way to determine the appropriate dosage is to assesscardiovascular changes (for example by ECG and blood pressuremonitoring) at or around the EC₅₀ value of the pro-drug and/or theactive metabolite (resulting in vivo following dosing of the pro-drug),for an adenosine receptor (preferably the receptor for which it/theyhas/have highest affinity) to determine the maximum tolerated dose. Thetherapeutically effective dose is then expected to be one ten thousandthto one half (or one ten thousandth to one fifth, or one ten thousandthto one twentieth, or one ten thousandth to one hundredth, or one tenthousandth to one thousandth, or one thousandth to one half, or onethousandth to one fifth, or one thousandth to one twentieth, or onefiftieth to one tenth, or one hundredth to one half, or one hundredth toone fifth, or one fiftieth to one half, or one fiftieth to one third, orone fiftieth to one fifth, or one tenth to one half, or one tenth to onefifth) of the maximum tolerated dose.

WO 2005/084653 shows that for spongosine the dose should be less than 28mg in humans. This dose gives rise to plasma concentrations between 0.5and 0.9 μM (close to the K_(d) at adenosine A2A receptors at pH 7.4 seebelow). Based on this result, the preferred dosage range for spongosineis 0.03 to 0.3 mg/kg. The preferred dosage range of the pro-drugs of theinvention is 0.03 to 8 mg/kg.

The minimum plasma concentration of spongosine giving maximal analgesicrelief in a rat adjuvant model of arthritis was 0.06 μM, considerablyless than the EC₅₀ of spongosine at the adenosine A2A receptor which isapproximately 1 μM. The preferred dosing levels in humans give maximumplasma concentrations between 0.005 and 0.5 μM which are significantlylower than those expected to give an analgesic or an anti-inflammatoryeffect by an action on this receptor.

Alternatively, appropriate therapeutic concentrations of the activemetabolites (resulting, in vivo, following dosing of the pro-drugs ofthe invention) are expected to be approximately 10-20 times the K_(i)for an adenosine receptor (the receptor for which the active metabolitehas the highest affinity) at pH 5.5. Thus, for spongosine 15 to 30 nM isrequired whereas using the K_(i) at pH7.4 the concentration that isexpected to be required is 20 to 30 μM.

It is expected that the amount of a pro-drug of the invention that isadministered should be 0.001-15 mg/kg. The amount may be less than 6mg/kg. The amount may be at least 0.001, 0.01, 0.1, or 0.2 mg/kg. Theamount may be less than 0.1, or 0.01 mg/kg. Preferred ranges are0.001-10, 0.001-5, 0.001-2, 0.001-1, 0.001-0.1, 0.001-0.01, 0.01-15,0.01-10, 0.01-5, 0.01-2, 0.01-1, 0.1-10, 0.1-5, 0.1-2, 0.1-1, 0.1-0.5,0.1-0.4, 0.2-15, 0.2-10, 0.2-5, 0.2-2, 0.2-1.2, 0.2-1, 0.6-1.2, mg/kg.

Preferred doses for a human subject (for example a 70 kg subject) areless than 420 mg, preferably less than 28 mg, more preferably less than21 mg, and preferably at least 0.07, 0.1, 0.7, or 0.8 mg, morepreferably at least 3.5 or 7 mg. More preferably 7-70 mg, 14-70 mg, or3.5-21 mg.

It is believed that the dosage amounts specified above are significantlylower (up to approximately 5000 times lower) than would be expected tobe required for an analgesic or an anti-inflammatory effect based on theEC₅₀ value of the compound at the adenosine A2A receptor.

The preferred dosage amounts specified above are aimed at producingplasma concentrations of active metabolites (resulting, in vivo,following dosing of the pro-drugs of the invention), that areapproximately one hundredth to one half of the EC₅₀ value of the activemetabolite at the adenosine receptor for which it has highest affinity.

A pro-drug of the invention may be administered with or without othertherapeutic agents, for example analgesics or anti-inflammatories (suchas opiates, steroids, NSAIDs, cannabinoids, tachykinin modulators, orbradykinin modulators) or anti-hyperalgesics (such as gabapentin,pregabalin, cannabinoids, sodium or calcium channel modulators,anti-epileptics or anti-depressants), or DMARDs.

In general, a pro-drug of the invention may be administered by knownmeans, in any suitable formulation, by any suitable route. A pro-drug ofthe invention is preferably administered orally, parenterally,sublingually, transdermally, intrathecally, or transmucosally. Othersuitable routes include intravenous, intramuscular, subcutaneous,inhaled, and topical. The amount of drug administered will typically behigher when administered orally than when administered, say,intravenously.

It will be appreciated that a pro-drug of the invention may beadministered together with a physiologically acceptable carrier,excipient, or diluent.

To maintain therapeutically effective plasma concentrations for extendedperiods of time, pro-drugs of the invention may be incorporated intoslow release formulations.

Suitable compositions, for example for oral administration, includesolid unit dose forms, and those containing liquid, e.g. for injection,such as tablets, capsules, vials and ampoules, in which the active agentis formulated, by known means, with a physiologically acceptableexcipient, diluent or carrier. Suitable diluents and carriers are known,and include, for example, lactose and talc, together with appropriatebinding agents etc.

A unit dosage of a pro-drug of the invention typically comprises up to500 mg (for example 1 to 500 mg, or (preferably) 5 to 500 mg) of theactive agent (pro-drug). Preferably the active agent is in the form of apharmaceutical composition comprising the active agent and aphysiologically acceptable carrier, excipient, or diluent. Preferreddosage ranges (i.e. preferred amounts of the active ingredient in a unitdose) are 0.001-10, 0.001-5, 0.001-2, 0.001-1, 0.001-0.1, 0.001-0.01,0.01-15, 0.01-10, 0.01-5, 0.01-2, 0.01-1, 0.1-10, 0.1-5, 0.1-2, 0.1-1,0.1-0.5, 0.1-0.4, 0.2-15, 0.2-10, 0.2-5, 0.2-2, 0.2-1.2, 0.2-1, 0.5 to1, 0.6-1.2, typically about 0.2 or 0.6, mg of the active agent per kg ofthe (human) subject. Preferred amounts of the active agent are less than420 mg, preferably less than 28 mg, more preferably less than 21 mg, andpreferably at least 0.07, 0.1, 0.7 or 0.8 mg, more preferably at least3.5 or 7 mg. More preferably 7 to 70 mg, or 14 to 70 mg, 3.5 to 21 mg,0.07-0.7 mg, or 0.7-7 mg. At these levels, it is believed that effectivetreatment can be achieved substantially without a concomitant fall (forexample, no more than 10%) in blood pressure and/or increase incompensatory heart rate.

A unit dosage of a pro-drug of the invention may further comprise one ormore other therapeutic agents, for example analgesics,anti-inflammatories, anti-hyperalgesics, or DMARDs.

Preferably a pro-drug of the invention is administered at a frequency of2 or 3 times per day.

Pro-drugs of the invention can also serve as a basis for identifyingmore effective drugs, or drugs that have further reduced side effects.

The following definitions shall apply throughout the specification andthe appended claims.

The term “C₁₋₆-alkyl” denotes a straight or branched alkyl group havingfrom 1 to 6 carbon atoms. Examples of said lower alkyl include methyl,ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, t-butyl andstraight- and branched-chain pentyl and hexyl. For parts of the range“C₁₋₆-alkyl” all subgroups thereof are contemplated such as C₁₋₅-alkyl,C₁₋₄-alkyl, C₁₋₃-alkyl, C₁₋₂-alkyl, C₂₋₆-alkyl, C₂₋₅-alkyl, C₂₋₄-alkyl,C₂₋₃-alkyl, C₃₋₆-alkyl, C₄₋₅-alkyl, etc.

The term “C₃₋₈-cycloalkyl” denotes a cyclic alkyl group having a ringsize from 3 to 8 carbon atoms. Examples of said cycloalkyl includecyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, methylcyclohexyl,cycloheptyl, and cyclooctyl. For parts of the range “C₃₋₈-cycloalkyl”all subgroups thereof are contemplated such as C₃₋₇-cycloalkyl,C₃₋₆-cycloalkyl, C₃₋₅-cycloalkyl, C₃₋₄-cycloalkyl, C₄₋₈-cycloalkyl,C₄₋₇-cycloalkyl, C₄₋₆-cycloalkyl, C₄₋₅-cycloalkyl, C₅₋₇-cycloalkyl,C₆₋₇-cycloalkyl, etc.

The term “halogen” shall mean fluorine, chlorine, bromine or iodine.

The term “aryl” refers to a hydrocarbon ring system having at least onearomatic ring. Examples of aryls are phenyl, pentalenyl, indenyl,indanyl, isoindolinyl, chromanyl, naphthyl, fluorenyl, anthryl,phenanthryl and pyrenyl. The aryl rings may optionally be substitutedwith C₁₋₆-alkyl. Examples of substituted aryl groups are 2-methylphenyland 3-methylphenyl.

The term “heteroaryl” means in the present description a monocyclic, bi-or tricyclic aromatic ring System (only one ring need to be aromatic)having from 5 to 14, preferably 5 to 10 ring atoms such as 5, 6, 7, 8, 9or 10 ring atoms (mono- or bicyclic), in which one or more of the ringatoms are other than carbon, such as nitrogen, sulfur, oxygen andselenium as part of the ring System. Examples of such heteroaryl ringsare pyrrole, imidazole, thiophene, furan, thiazole, isothiazole,thiadiazole, oxazole, isoxazole, oxadiazole, pyridine, pyrazine,pyrimidine, pyridazine, pyrazole, triazole, tetrazole, chroman,isochroman, quinoline, quinoxaline, isoquinoline, phthalazine,cinnoline, quinazoline, indole, isoindole, indoline (i e2,3-dihydroindole), isoindoline (i e 1,3-dihydroisoindole),benzothiophene, benzofuran, 2,3-dihydrobenzofuran, isobenzofuran,benzodioxole, benzothiadiazole, benzotriazole, benzoxazole,2,1,3-benzoxadiazole, benzopyrazole, 2,1,3-benzothiazole,2,1,3-benzoselenadiazole, benzimidazole, indazole, benzodioxane,2,3-dihydro-1,4-benzodioxine, indane, 1,2,3,4-tetrahydroquinoline,3,4-dihydro-2H-1,4-benzoxazine, 1,5-naphthyridine, 1,8-naphthyridine,pyrido[3,2-b]thiophene, acridine, fenazine and xanthene.

The term “heterocyclic” and “heterocyclyl” in the present description isintended to include unsaturated as well as partially and fully saturatedmono-, bi- and tricyclic rings having from 4 to 14, preferably 4 to 10ring atoms having one or more heteroatoms (e.g., oxygen, sulfur, ornitrogen) as part of the ring System and the reminder being carbon, suchas, for example, the heteroaryl groups mentioned above as well as thecorresponding partially saturated or fully saturated heterocyclic rings.Exemplary saturated heterocyclic rings are azetidine, pyrrolidine,piperidine, piperazine, morpholine, thiomorpholine, 1,4-oxazepane,azepane, phthalimide, indoline, isoindoline,1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroisoquinoline,hexahydroazepine, 3,4-dihydro-2(1H)isoquinoline, 2,3-dihydro-1H-indole,1,3-dihydro-2H-isoindole, azocane, 1-oxa-4-azaspiro[4.5]dec-4-ene,decahydroisoquinoline, 1,2-dihydroquinoline, and 1,4-diazepane.

“Pharmaceutically acceptable” means being useful in preparing apharmaceutical composition that is generally safe, non-toxic and neitherbiologically nor otherwise undesirable and includes being useful forveterinary use as well as human pharmaceutical use.

“Treatment” as used herein includes prophylaxis of the named disorder orcondition, or amelioration or elimination of the disorder once it hasbeen established.

“An effective amount” refers to an amount of a compound that confers atherapeutic effect on the treated subject. The therapeutic effect may beobjective (i.e., measurable by some test or marker) or subjective (i.e.,subject gives an indication of or feels an effect).

The term “prodrug forms” means a pharmacologically acceptablederivative, such as an ester or an amide, which derivative isbiotransformed in the body to form the active drug.

Reference is made to Goodman and Gilman's, The Pharmacological basis ofTherapeutics, 8^(th) ed., Mc-Graw-Hill, Int. Ed. 1992,“Biotransformation of Drugs”, p. 13-15.

The term “active metabolite” means the pharmacologically active compoundreleased following metabolism of the pro-drug in-vivo.

The following abbreviations have been used:

Aq Aqueous

Ar Aryl

Bz Benzoyl

DCM Dichloromethane

DMARD Disease modifying antirheumatic drug

EC50 50% Effective concentration

EDTA ethylenediaminetetraacetic acid

ES⁺ Electrospray

EtOAc Ethyl acetate

HIV Human immunodeficiency virus

HPLC High performance liquid chromatography

IV Intravenous

JV Jugular vein

Kd Dissociation constant

LCMS Liquid chromatography mass spectrometry

M Molar

[MH⁺] Protonated molecular ion

RP Reverse phase

Me Methyl

MS Mass spectrometry

NSAID Non steroidal anti-inflammatory drug

PK Pharmacokinetic

PO Per oral

PSA Polar surface area

RA Rheumatoid arthritis

SD Sprague Dawley

THF Tetrahydrofuran

TMAN Tetramethylammonium nitrate

TFA Trifluoroacetic acid

TFAA Trifluoroacetic anhydride

All isomeric forms possible (pure enantiomers, diastereomers, tautomers,racemic mixtures and unequal mixtures of two enantiomers) for thecompounds delineated within the scope of the invention. Such compoundscan also occur as cis- or trans-, E- or Z-double bond isomer forms. Allisomeric forms are contemplated.

The compounds of Formula (I) may be used as such or, where appropriate,as pharmacologically acceptable salts (acid or base addition salts)thereof. The pharmacologically acceptable addition salts mentioned aboveare meant to comprise the therapeutically active non-toxic acid and baseaddition salt forms that the compounds are able to form. Compounds thathave basic properties can be converted to their pharmaceuticallyacceptable acid addition salts by treating the base form with anappropriate acid. Exemplary acids include inorganic acids, such ashydrogen chloride, hydrogen bromide, hydrogen iodide, sulfuric acid,phosphoric acid; and organic acids such as formic acid, acetic acid,propanoic acid, hydroxyacetic acid, lactic acid, pyruvic acid, glycolicacid, maleic acid, malonic acid, oxalic acid, benzenesulfonic acid,toluenesulfonic acid, methanesulfonic acid, trifluoroacetic acid,fumaric acid, succinic acid, malic acid, tartaric acid, citric acid,salicylic acid, p-aminosalicylic acid, pamoic acid, benzoic acid,ascorbic acid and the like. Exemplary base addition salt forms are thesodium, potassium, calcium salts, and salts with pharmaceuticallyacceptable amines such as, for example, ammonia, alkylamines,benzathine, and amino acids, such as, e.g. arginine and lysine. The termaddition salt as used herein also comprises solvates which the compoundsand salts thereof are able to form, such as, for example, hydrates,alcoholates and the like.

For clinical use, the compounds of the invention are formulated intopharmaceutical formulations for oral, rectal, parenteral or other modeof administration. Pharmaceutical formulations are usually prepared bymixing the active substance, or a pharmaceutically acceptable saltthereof, with conventional pharmaceutical excipients. Examples ofexcipients are water, gelatin, gum arabicum, lactose, microcrystallinecellulose, starch, sodium starch glycolate, calcium hydrogen phosphate,magnesium stearate, talcum, colloidal silicon dioxide, and the like.Such formulations may also contain other pharmacologically activeagents, and conventional additives, such as stabilizers, wetting agents,emulsifiers, flavouring agents, buffers, and the like.

The formulations can be further prepared by known methods such asgranulation, compression, microencapsulation, spray coating, etc. Theformulations may be prepared by conventional methods in the dosage formof tablets, capsules, granules, powders, syrups, suspensions,suppositories or injections. Liquid formulations may be prepared bydissolving or suspending the active substance in water or other suitablevehicles. Tablets and granules may be coated in a conventional manner.

In a further aspect the invention relates to methods of making compoundsof any of the formulae herein comprising reacting any one or more of thecompounds of the formulae delineated herein, including any processesdelineated herein. The compounds of Formula (I) above may be preparedby, or in analogy with, conventional methods.

The processes described above may be carried out to give a compound ofthe invention in the form of a free base or as an acid addition salt. Apharmaceutically acceptable acid addition salt may be obtained bydissolving the free base in a suitable organic solvent and treating thesolution with an acid, in accordance with conventional procedures forpreparing acid addition salts from base compounds. Examples of additionsalt forming acids are mentioned above.

The compounds of Formula (I) may possess one or more chiral carbonatoms, and they may therefore be obtained in the form of opticalisomers, e.g., as a pure enantiomer, or as a mixture of enantiomers(racemate) or as a mixture containing diastereomers. The separation ofmixtures of optical isomers to obtain pure enantiomers is well known inthe art and may, for example, be achieved by fractional crystallizationof salts with optically active (chiral) acids or by chromatographicseparation on chiral columns.

The chemicals used in the synthetic routes delineated herein mayinclude, for example, solvents, reagents, catalysts, and protectinggroup and deprotecting group reagents. The methods described above mayalso additionally include steps, either before or after the stepsdescribed specifically herein, to add or remove suitable protectinggroups in order to ultimately allow synthesis of the compounds. Inaddition, various synthetic steps may be performed in an alternatesequence or order to give the desired compounds. Synthetic chemistrytransformations and protecting group methodologies (protection anddeprotection) useful in synthesizing applicable compounds are known inthe art and include, for example, those described in R. Larock,Comprehensive Organic Transformations, VCH Publishers (1989); T. W.Greene and P. G. M. Wuts, Protective Groups in Organic Synthesis, 3^(rd)Ed., John Wiley and Sons (1999); L. Fieser and M. Fieser, Fieser andFieser's Reagents for Organic Synthesis, John Wiley and Sons (1994); andL. Paquette, ed., Encyclopedia of Reagents for Organic Synthesis, JohnWiley and Sons (1995) and subsequent editions thereof.

The necessary starting materials for preparing the compounds of Formula(I) are either known or may be prepared in analogy with the preparationof known compounds.

Embodiments of the invention are described in the following exampleswith reference to the accompanying drawing in which:

FIG. 1 shows the effect of spongosine on the maintenance of streptozocin(STZ)-induced diabetic neuropathy as measured by static allodynia.

The recitation of a listing of chemical groups in any definition of avariable herein includes definitions of that variable as any singlegroup or combination of listed groups. The recitation of an embodimentfor a variable herein includes that embodiment as any single embodimentor in combination with any other embodiments or portions thereof.

The specific examples below are to be construed as merely illustrative,and not limitative of the remainder of the disclosure in any waywhatsoever. Without further elaboration, it is believed that one skilledin the art can, based on the description herein, utilize the presentinvention to its fullest extent. All publications cited herein arehereby incorporated by reference in their entirety.

Experimental Methods

All reagents were commercial grade and were used as received withoutfurther purification, unless otherwise specified. Reagent grade solventswere used in all cases. The 2-iodo adenosine was supplied by GeneralIntermediates of Canada, Inc

Electrospray mass spectrometry (MS) was obtained using a waters ZQ massspectrometer. Analytical HPLC were performed on Agilent 1100 systemequipped with Phenomenex Synergi Hydro RP (C18, 150×4.6 mm) using theeluent system: water/0.1% TFA and CH₃CN, 1.5 mL/min, with a gradienttime of 7 min for both HPLC and LC-MS.

EXAMPLES Example 1 Preparation of(2R,3R,4R,5R)-5-(6-amino-2-methoxy-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol1

To a solution of 2′-methoxy adenosine (10 g, 35.6 mmol) in pyridine (75mL) was added benzoyl chloride (22.7 mL, 196 mmol) and the resultingsolution was refluxed at 80° C. for 4 h. The solvents were removed invacuo and the residue dissolved in EtOAc and washed with aq. NaHCO₃,brine and water, and the organic phase dried over MgSO₄. Crystallisationfrom ethanol afforded 26 as a white solid in 2 batches (13.7 g and 4.3g, 72% overall).

To a suspension of 26 (13.7 g, 19.7 mmol) and TMAN (3.48 g, 25.6 mmol)in DCM (100 mL) was added drop-wise a solution of TFAA (3.77 mL, 26.7mmol) in DCM (20 mL) and the resulting solution stirred for 2 h. Thesolution was then washed with aq. NaHCO₃ and water (×3) and the organicphase dried over MgSO₄. The residue was dissolved in ethanol (20 mL),DCM (50 mL) was added and the solvents were removed in vacuo to yield 27as a pale yellow foam (14 g, 96%, ˜70% purity by LCMS) which was usedwithout further purification.

To a solution of 27 (3.7 g, 5.31 mmol) in methanol (70 mL) was addedNaOMe (1.15 g, 21.3 mmol) and the resulting solution stirred at roomtemperature for 2 d. Silica gel (15 g) was then added and the solventsremoved in vacuo. Purification by flash column chromatography (normalphase, ICN silica, 18-32μ, gradient 10% ethanol in DCM, residue dryloaded) and recrystallisation from hot water afforded(2R,3R,4R,5R)-5-(6-amino-2-methoxy-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol1 as a white crystalline solid (536 mg, 32%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7min—held for 30 s, 200-300 nm): Retention time 2.80-2.86 min (splitpeak), 100%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 3.42 min, 100%, ES⁺:312.06 [MH]⁺.

Example 2 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-(2,2-difluoroethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol2

To a solution of 2,2-difluoroethanol (0.165 mL, 2.60 mmol) in THF (10mL) was added NaH (104 mg, 60% dispersion in mineral oil, 2.60 mmol) andthe resulting suspension stirred for 1 h. A solution of 27 (956 mg, 1.37mmol) in THF (10 mL) was then added and the resulting solution stirredat room temperature for 2 d. The solvents were then removed in vacuo andthe residue dissolved in methanol (20 mL) before the addition of NaOMe(cat) and stirring of the resulting suspension for 16 h. The solventswere removed in vacuo and the residue purified by flash columnchromatography (normal phase, ICN silica, 50 g, 18-32μ, gradient 2.5-15%ethanol in DCM, residue dry loaded, product eluted in 10-15% ethanol)and by reverse phase prep HPLC (Phenomenex Synergi, RP-Hydro 150×10 mm,10μ, 20 mL per min, gradient 5-45% acetonitrile in water over 10 min,product eluted in 25% acetonitrile) to yield(2R,3R,4R,5R)-5-[6-amino-2-(2,2-difluoroethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol2 as a white solid (134 mg, 27%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 3.42 min, 100%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 3.96 min, 100%, ES⁺:362.34 [MH]⁺.

Example 3 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-(cyclopentylmethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol3

To a solution of cyclopentanemethanol (1.73 mL, 19.1 mmol) in THF (35mL) was added NaH (637 mg, 60% dispersion in mineral oil, 15.9 mmol) andthe resulting suspension stirred for 1 h. A solution of 27 (3.7 g, 5.31mmol) in THF (35 mL) was then added and the resulting solution stirredat room temperature for 2 d. The solvents were then removed in vacuo andthe residue dissolved in methanol (70 mL) before the addition of NaOMe(860 mg, 15.9 mmol) and stirring of the resulting suspension for 16 h.Silica gel (15 g) was then added and the solvents removed in vacuo.Purification by flash column chromatography (normal phase, ICN silica,18-32μ, gradient 5-10% ethanol in DCM, residue dry loaded) andrecrystallisation from methanol/water afforded(2R,3R,4R,5R)-5-[6-amino-2-(cyclopentylmethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol3 as a white crystalline solid (356 mg, 18%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.27 min, 99.05%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.76 min, 100%, ES⁺:380.50 [MH]⁺.

Example 4 Preparation of(2R,3R,4R,5R)-5-{6-amino-2-[(2,2,3,3-tetrafluorocyclobutyl)oxy]-9H-purin-9-yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol4

To a solution of 2,2,3,3-tetrafluorocyclobutanol (265 μL, 2.60 mmol) inTHF (10 mL) was added NaH (104 mg, 60% dispersion in mineral oil, 2.60mmol) and the resulting suspension stirred for 1 h. A solution of 27(956 mg, 1.30 mmol) in THF (10 mL) was then added and the resultingsolution stirred at room temperature for 2 d. The solvents were thenremoved in vacuo and the residue dissolved in methanol (20 mL) beforethe addition of NaOMe (cat) and stirring of the resulting suspension for16 h. The solvents were removed in vacuo and the residue purified byflash column chromatography (normal phase, ICN silica, 50 g, 18-32μ,gradient 5-20% ethanol in DCM, residue dry loaded) and by reverse phasecolumn chromatography (LiChroprep RP-18, 40-63 μm, 460×26 mm (10 g), 30mL per min, gradient 0-100% methanol in water over 45 min, producteluted in 65% methanol) to yield(2R,3R,4R,5R)-5-{6-amino-2-[(2,2,3,3-tetrafluorocyclobutyl)oxy]-9H-purin-9yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol4 as a white solid (56 mg, 10%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300nm): Retention time 4.41 min, 99.13%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.83 min, 100%, ES⁺:424.36 [MH]⁺.

Example 5 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-(2,5-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol5

To a solution of 2,5-difluorophenol (104 mg, 0.80 mmol) in THF (7 mL)was added KO^(t)Bu (63 mg, 0.56 mmol) and the resulting suspensionstirred for 30 min before the addition of 27 (295 mg, 0.42 mmol).Stirring was continued for 6 h and the solvents were then removed invacuo. The residue was dissolved in methanol (7 mL), NaOMe (86 mg, 1.59mmol) was added and the resulting mixture was stirred for 16 h, beforebeing quenched with 10% aq. citric acid. The solvents were removed invacuo and the residue purified by reverse phase column chromatography(LiChroprep RP-18, 40-63 μm, 230×26 m (50 g), 30 mL per min, gradient40-80% methanol in water over 45 min, product eluted in 57% methanol)and reverse phase prep HPLC (Phenomenex Synergi, RP-Hydro 150×10 mm,10μ, 20 mL per min, gradient 15-30% acetonitrile in water over 10 min,product eluted in 26% acetonitrile) to yield(2R,3R,4R,5R)-5-[6-amino-2-(2,5-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol5 as a pale yellow solid (31 mg, 18%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.20 min, 99.00%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 5.91 min, 100%, ES⁺:410.48 [MH]⁺.

Example 6 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-(3,4-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol6

To a solution of 3,4-difluorophenol (338 mg, 2.60 mmol) in THF (10 mL)was added KO^(t)Bu (292 mg, 2.60 mmol) and the resulting suspensionstirred for 30 min before the addition of 27 (956 mg, 1.30 mmol).Stirring was continued for 2 d and the solvents were then removed invacuo. The residue was dissolved in methanol (20 mL), NaOMe (cat.) wasadded and the resulting mixture was stirred for 16 h and thenconcentrated in vacuo. Purification by flash column chromatography(normal phase, ICN silica, 50 g, 18-32μ, gradient 5-15% ethanol in DCM,residue dry loaded) and by reverse phase column chromatography(LiChroprep RP-18, 40-63 μm, 460×26 mm (100 g), 30 mL per min, gradient0-100% methanol in water over 45 min, product eluted in 55% methanol)afforded(2R,3R,4R,5R)-5-[6-amino-2-(3,4-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol6 as a white solid (188 mg, 36%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.40 min, 99.88%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.83 min, 100%, ES⁺:410.37 [MH]⁺.

Example 7 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-[4-chloro-3-(trifluoromethyl)phenoxy]-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol7

To a solution of 4-chloro-3-(trifluoromethyl)phenol (2.60 g, 13.2 mmol)in THF (100 mL) was added KO^(t)Bu (1.48 g, 13.2 mmol) and the resultingsuspension stirred for 30 min before the addition of 27 (4.93 g, 6.64mmol) as a suspension in THF (100 mL). Stirring was continued for 3 dand the solvents were then removed in vacuo. The residue was dissolvedin methanol (200 mL), NaOMe (1.07 g, 19.8 mmol) was added and theresulting mixture was stirred for 16 h. Silica gel (15 g) was then addedand the solvents were removed in vacuo. Purification by flash columnchromatography (normal phase, ICN silica, 70 g, 18-32μ, gradient 10-20%ethanol in DCM, residue dry loaded) and by reverse phase columnchromatography (LiChroprep RP-18, 40-63 μm, 460×26 mm (10 g), 30 mL permin, gradient 50-100% methanol in water over 45 min, product eluted in70% methanol) and by reverse phase prep HPLC (Phenomenex Synergi,RP-Hydro 150×10 mm 10μ, 20 mL per min, gradient 30-50% acetonitrile inwater over 10 min) in 6 batches afforded(2R,3R,4R,5R)-5-[6-amino-2-[4-chloro-3-(trifluoromethyl)phenoxy]-9H-purin-9-yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol7 as a white solid (708 mg, 22%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 5.22 min, 100%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 5.57 min, 100%, ES⁺:475.98 [MH]⁺.

Example 8 Preparation of(2R,3R,4R,5R)-5-(6-amino-2-{[(1S)-1-methylpropyl]amino}-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol8

To a solution of 27 (445 mg, 0.64 mmol) in THF (8 mL) was added(S)-sec-butylamine (120 μL, 1.18 mmol) and further THF (8 mL). Stirringwas continued for 1 wk and the solvents were then removed in vacuo. Theresidue was dissolved in methanol (8 mL), NaOMe (cat) was added and theresulting mixture was stirred for 2 d. Further NaOMe (cat) was added andthe resulting mixture was stirred for 1 d before being concentrated invacuo. The residue was dissolved in acetonitrile/water (1:1, 3 mL) andTFA/water (1:1, 0.5 mL) was added. This solution was purified by reversephase column chromatography (LiChroprep RP-18, 40-63 μm, 230×26 mm 50g), 30 mL per min, gradient 0-75% methanol in water over 30 min) andreverse phase prep HPLC (Phenomenex Synergi, RP-Hydro 150×10 mm, 10μ, 20mL per min, gradient 5-45% acetonitrile in water over 10 min, producteluted in 37% acetonitrile) in 2 batches to yield(2R,3R,4R,5R)-5-(6-amino-2-{[(1S)-1-methylpropyl]amino}-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol8 as a white solid (6.5 mg, 3%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 3.54 min, 99.23%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 4.52 min, 98.40%, ES⁺:353.43 [MH]⁺.

Example 9 Preparation of(2R,3R,4R,5R)-5-[6-amino-2-(cyclohexylamino)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol9

To a solution of 27 (5.22 mg, 7.0 mmol) in THF (50 mL) was addedcyclohexylamine (1.93 mL, 16.8 mmol) and stirring was continued for 16h. The solvents were then removed in vacuo. The residue was dissolved inmethanol (8 mL), NaOMe (1.09 g, 20.2 mmol) was added and the resultingmixture was stirred for 16 h, before being quenched with 10% aq. citricacid (10 mL). 10 g silica gel was then added and the solvents wereremoved in vacuo and the residue purified by flash column chromatography(normal phase, ICN silica, 50 g, 18-32μ, gradient 5-25% ethanol in DCM,residue dry loaded) and by reverse phase column chromatography(LiChroprep RP-18, 40-63 μm, 460×26 mm (100 g), 30 mL per min, gradient40-90% methanol in water over 45 min) to yield(2R,3R,4R,5R)-5-[6-amino-2-(cyclohexylamino)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol9 as a white solid (51 mg). Concentration of the impure fractions andcrystallization from methanol/water afforded further 9 as colorlessneedles (95 mg, overall yield 6%).

HPLC (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 3.91 min, 99.76%.

LCMS (Phenomenex Synergi, RP-Hydro, 150×4.6 mm, 4 u, 1.5 mL per min, 30°C., gradient 5-100% acetonitrile (+0.085% TFA) in water (+0.1% TFA) over7 min—held for 30 s, 200-300 nm): Retention time 5.11 min, 100%, ES⁺:379.5 [MH]⁺.

Active Metabolites

Structures of the expected in vivo active metabolites, corresponding tothe pro-drugs described in Examples 1 to 9, are given in Table I below.TABLE 1 Prodrug Active metabolite Example No. Structure Reference 1

WO 2005/084653 Compound 1 (Spongosine) 2

WO 2005/084653 Compound 2 3

WO 2005/084653 Compound 32 4

WO 2005/084653 Compound 35 5

WO 2005/084653 Compound 9 6

WO 2005/084653 Compound 11 7

8

WO 2005/084653 Compound 23 9

WO 2005/084653 Compound 30

Biological Methods

The Pharmacokinetics of adenosine derivatives was studied in vivo usingJV-cannulated SD rats. Dose samples were either of a single compound ina suitable formulation, or a mix of 5-7 varied compounds. The animalswere dosed IV (n=4) and PO via gavage tube (n=4), and blood samples (200μl) taken at pre-dose, 5, 10, 20, 30, 45, 60, 120, 240, 360 min (IV) orpre-dose, 5, 10, 20, 45, 60, 120, 240, 360, 1440 min (PO). Samples weretaken into EDTA anti-coagulant and centrifuged. The resultant plasma wasstored at −80° C. prior to analysis.

Plasma was extracted either by solid phase extraction or by proteinprecipitation. After drying, reconstitution in appropriate solvent,centrifugation and isolation of the supernatant, the samples (n=3: IVand PO) were analyzed by High Performance Liquid Chromatography-MassSpectrometry, using MS/MS Selected Reaction Monitoring for optimumsensitivity and selectivity. The plasma drug levels were mathematicallyanalyzed using a non-compartmental PK calculation, with AUC's derived bythe linear trapezoidal method. Half-lives were calculated by a best-fitto the terminal phase as adjudged by the user.

Results: For a range of nine 2-substituted adenosines, the oralbioavailability was found to increase on average from 12% to 40% and theoral half-life from 0.8 h to 1.5 h by employing a 2′-methoxy pro-drugstrategy.

Consequently, it is believed that by using the novel pro-drug strategydescribed herein, the oral bioavailability and oral half-life of theseadenosine derivatives can be significantly increased. This isparticularly surprising, since nucleoside derivatives tend to be polarmolecules with high polar surface areas (PSAs) (e.g. adenosine 140 Å²,guanosine 160 Å², cytidine 131 Å², uridine 125 Å², PSAs calculatedaccording to the procedure described in Ertl, Rohde and Selzer (2000) J.Med. Chem. 43, 3714). PSA has been shown to be a very good descriptorcharacterising drug absorption, including intestinal absorption,bioavailability, Caco-2 permeability and blood-brain barrierpenetration. PSAs are calculated computationally using moleculartopology, based on the summation of tabulated surface contributions ofpolar fragments (Ertl, Rohde and Selzer (2000) J. Med. Chem. 43, 3714).

Palm et al. (Pharm. Res. (1997) 14, 568) have demonstrated a Boltzmannsigmoidal fit of PSA values to human F % over a wide range of structuresand have demonstrated that typically, in order for compounds to be atleast 20% bioavailable, the PSA should be <120 Å² and for at least 50%oral bioavailability, the PSA should be <95 Å².

The 2′-methoxy pro-drugs described herein have an average PSA of 138 Å²(calculated as above) and would therefore be expected to be poorlyorally bioavailable (<10% F) (Clark, J. Pharm. Sci. (1999) 88, 807).Surprisingly these pro-drugs have an average of 40% oralbioavailability.

Example 10

The anti-allodynic potential of orally administered spongosine wasdetermined using rats experiencing streptozocin-induced diabeticneuropathy. Diabetes was induced by a single i.p. injection of 50 mg/kgstreptozocin (Sigma, 50 mg/ml/kg in citrate buffered saline 33 mM pH4.5). Control animals received single i.p. injection of citrate bufferedsaline. Static allodynia and diabetes could be detected from day 7 postSTZ injection and were present in the majority of animals by day 14 withanimals consistently demonstrating a paw withdrawal threshold (PWT) tothe previously innocuous 3.63 g or lower force. Static allodynia wastested by touching the plantar surface of hind paws with Von Frey hairs(Semmes Weinstein series) in ascending order of force (0.7, 1.2, 1.5, 2,3.6, 5.5, 8.5, 11.8, 15.1, and 29 g) for up to 6 s. The anti-allodynicpotential of spongosine (0.6-2.08 mg/kg po) orally administered wasexamined in STZ diabetic animals once static allodynia had developed(between 20-35 days post streptozocin injection).

FIG. 1 shows that spongosine exhibited dose dependant effects (0.6-2.1mg/kg, po) on the reversal of streptozocin induced static allodynia. Alldoses were effective at reversing allodynia, whilst the top dose fullyreversed the allodynia to levels exhibited by naïve non-streptozocininjected control animals. Static allodynia was assessed using von Freyhairs and the paw withdrawal threshold (PWT) in grams (symbols representthe median and vertical bars represent the first and third quartiles) isindicated. All doses of spongosine tested alleviated static allodyniaresulting in an increase in the PWT i.e. in the ability of the animal towithstand increased pressure exerted by the von Frey hairs. **p<0.01,*p<0.05 significantly different (Mann-Whitney U test) comparing drugtreated STZ group to vehicle treated STZ group at each time point.Significant alleviation of allodynia was still evident in the 2.1 mg/kgdose cohort at 2, 3 and 4 hours.

1. A method of treating or preventing a subject having or at risk of amedical condition that can be improved or prevented by agonism orantagonism of an adenosine receptor comprising administration to thesubject a compound of Formula I, or a pharmaceutically acceptable saltthereof,

wherein: R1 is adenine, which is unsubstituted or substituted with 1-3substituents independently selected from halogen, OH, OR4, NR4R5, CN,SR4 or R4; R2 is selected from CH₂OH, CH₂OR4, CH₂R4, R4, CH₂CO2R4,CH₂CONR4R5, CH₂NR4R5, CH₂halogen, CO₂R4, CONR4R5, CH₂OCOR4, CH₂OCONR4R5,CH₂NHCOR4 or CH₂NHCONR4R5; R3 is selected from F, OH, OR4, NH₂, N₃ orNR4R5; R4 and R5 are independently selected from H, C₁₋₆-alkyl,C₃₋₈-cycloalkyl, aryl or heterocyclyl, each optionally substituted with1-3 substituents independently selected from halogen, OH, NH₂, CN orCF₃.
 2. The method according to claim 1 wherein the said compound is ofthe formula II, or a pharmaceutically acceptable salt thereof,

wherein R1 is as described in claim
 1. 3. The method according to claim1 or 2 wherein the said medical condition can be improved or preventedby agonism of an adenosine receptor.
 4. The method according to claim 3wherein the said medical condition is associated with pain.
 5. Themethod according to claim 4 wherein the pain is hyperalgesia.
 6. Themethod according to claim 4 or 5 wherein the pain is caused byneuropathy.
 7. The method according to any of claims 4 to 6 wherein thepain is associated with Diabetic Neuropathy, Polyneuropathy,Sciatica/Lumbar Radiculopathy, Cancer Pain, Post Herpetic Neuralgia,Myofascial Pain Syndrome, Rheumatoid Arthritis, Fibromyalgia,Osteoarthritis, Pancreatic Pain, Pelvic/Perineal pain, Spinal Stenosis,Temporo-mandibular Joint Disorder, HIV pain, Trigeminal Neuralgia,Chronic Neuropathic Pain, Lower Back Pain, Failed Back Surgery pain,back pain, post-operative pain, post physical trauma pain (includinggunshot, road traffic accident, burns), Cardiac pain, Chest pain, Pelvicpain/PID, Neck Pain, Bowel Pain, Phantom Limb Pain, Obstetric Pain(labour/C-Section), Renal Colic, Acute Herpes Zoster Pain, AcutePancreatitis Breakthrough Pain (Cancer), Dysmenorhoea/Endometriosis; orin any of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition.
 8. The methodaccording to claim 4 or 5 wherein the pain is caused by inflammatorydisease, or by combined inflammatory, autoimmune and neuropathic tissuedamage.
 9. The method according to any of claims 4, 5 or 8 wherein thepain is associated with Rheumatoid Arthritis, Osteoarthritis, Joint pain(tendonitis, bursitis, acute arthritis), Lower Back Pain, Failed BackSurgery pain, back pain, post-operative pain, post physical trauma pain(including gunshot, road traffic accident, burns), Fibromyalgia,rheumatoid arthritis, spondylitis, gouty arthritis, and other arthriticconditions, cancer, HIV, Diabetic Neuropathy, Polyneuropathy,Sciatica/Lumbar Radiculopathy, autoimmune damage (including multiplesclerosis, Guillam Barre Syndrome, myasthenia gravis) graft v. hostrejection, allograft rejections, fever and myalgia due to infection,AIDS related complex (ARC), keloid formation, scar tissue formation,Crohn's disease, ulcerative colitis and pyresis, irritable bowelsyndrome, osteoporosis, cerebral malaria and bacterial meningitis, bowelpain, cancer pain, back pain, fibromyalgia, post-operative pain; or inany of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition.
 10. The methodaccording to claim 4 wherein the pain is ischaemic pain.
 11. The methodaccording to claim 4 or 10 wherein the pain is associated with coronaryartery disease, peripheral artery disease, and conditions which arecharacterized by insufficient blood flow, usually secondary toatherosclerosis left ventricular hypertrophy, essential hypertension,acute hypertensive emergency, cardiomyopathy, heart insufficiency,exercise tolerance, chronic heart failure, arrhythmia, cardiacdysrhythmia, syncopy, arteriosclerosis, mild chronic heart failure,angina pectoris, Prinzmetal's (variant) angina, stable angina, andexercise induced angina, cardiac bypass reocclusion, intermittentclaudication (arteriosclerosis oblitterens), arteritis, diastolicdysfunction and systolic dysfunction, atherosclerosis, postischaemia/reperfusion injury, diabetes (both Types I and II),thromboembolisms, and haemorrhagic accidents that also result inischaemic pain.
 12. The method according to claim 3 wherein the saidmedical condition is associated with inflammation.
 13. The methodaccording to claim 12 wherein the inflammation is caused by orassociated with cancer (such as leukemias, lymphomas, carcinomas, coloncancer, breast cancer, lung cancer, pancreatic cancer, hepatocellularcarcinoma, kidney cancer, melanoma, hepatic, lung, breast, and prostatemetastases, etc.); Chronic Obstructive Pulmonary Disease (COPD), acutebronchitis, chronic bronchitis, emphysema, bronchiectasis, cysticfibrosis, pneumonia, pleurisy, acute asthma, chronic asthma, acuterespiratory distress syndrome, adult respiratory distress syndrome(ARDS), infant respiratory distress syndrome (IRDS) acute lung injury(ALI), laryngitis, pharangitis, persistent asthma, chronic asthmaticbronchitis, interstitial lung disease, lung malignancies,alpha-anti-trypsin deficiency, bronchiolitis obliterans, sarcoidosis,pulmonary fibrosis, collagen vascular disorders, allergic rhinitis,nasal congestion, status asthmaticus, smoking related pulmonary disease,pulmonary hypertension, pulmonary oedema, pulmonary embolism, pleuraleffusion, pneumothorax, haemothorax, lung cancer, allergies, pollinosisHay fever), sneeze, vasomotor rhinitis, mucositis, sinusitis, exogenousirritant induced illness (SO₂, smog, pollution), airwayhypersensitivity, milk product intolerance, Luffer's pneumonia,pneumoconiosis, collagen induced vascular disease, granulomatousdisease, bronchial inflammation, chronic pulmonary inflammatory disease,bone resorption diseases, reperfusion injury (including damage caused toorgans as a consequence of reperfusion following ischaemic episodes e.g.myocardial infarcts, strokes), auto-immune disease (such as organtransplant rejection, lupus erythematosus, graft v. host rejection,allograft rejections, multiple sclerosis, rheumatoid arthritis, type Idiabetes mellitus including the destruction of pancreatic islets leadingto diabetes and the inflammatory consequences of diabetes); autoimmunedamage (including multiple sclerosis, Guillam Barre Syndrome, myastheniagravis); obesity; cardiovascular conditions associated with poor tissueperfusion and inflammation (such as atheromas, atherosclerosis, stroke,ischaemia-reperfusion injury, claudication, spinal cord injury,congestive heart failure, vasculitis, haemorrhagic shock, vasospasmfollowing subarachnoid haemorrhage, vasospasm following cerebrovascularaccident, pleuritis, pericarditis, the cardiovascular complications ofdiabetes); ischaemia-reperfusion injury, ischaemia and associatedinflammation, restenosis following angioplasty and inflammatoryaneurysms; epilepsy, neurodegeneration (including Alzheimer's Disease),muscle fatigue or muscle cramp (particularly athletes' cramp), arthritis(such as rheumatoid arthritis, osteoarthritis, rheumatoid spondylitis,gouty arthritis), fibrosis (for example of the lung, skin and liver),multiple sclerosis, sepsis, septic shock, encephalitis, infectiousarthritis, Jarisch-Herxheimer reaction, shingles, toxic shock, cerebralmalaria, Lyme's disease, endotoxic shock, gram negative shock,haemorrhagic shock, hepatitis (arising both from tissue damage or viralinfection), deep vein thrombosis, gout; conditions associated withbreathing difficulties (e.g. impeded and obstructed airways,bronchoconstriction, pulmonary vasoconstriction, impeded respiration,silicosis, pulmonary sarcosis, pulmonary hypertension, pulmonaryvasoconstriction, bronchial allergy and vernal conjunctivitis);conditions associated with inflammation of the skin (includingpsoriasis, eczema, ulcers, contact dermatitis); conditions associatedwith inflammation of the bowel (including Crohn's disease, ulcerativecolitis and pyresis, irritable bowel syndrome, inflammatory boweldisease); HIV (particularly HIV infection), cerebral malaria, bacterialmeningitis, TNF-enhanced HIV replication, TNF inhibition of AZT and DDIactivity, osteoporosis and other bone resorption diseases,osteoarthritis, rheumatoid arthritis, infertility from endometriosis,fever and myalgia due to infection, cachexia secondary to cancer,cachexia secondary to infection or malignancy, cachexia secondary toacquired immune deficiency syndrome (AIDS), AIDS related complex (ARC),keloid formation, scar tissue formation, adverse effects fromamphotericin B treatment, adverse effects from interleukin-2 treatment,adverse effects from OKT3 treatment, or adverse effects from GM-CSFtreatment, and other conditions mediated by excessive anti-inflammatorycell (including neutrophil, eosinophil, macrophage and T-cell) activity;or in any of the above pathological conditions where bacterial or viralinfection is a cause or exacerbates the condition, macro or microvascular complications of type 1 or 2 diabetes, retinopathy,nephropathy, autonomic neuropathy, or blood vessel damage caused byischaemia or atherosclerosis.
 14. The method according to claim 3wherein the said medical condition is associated with arthropathy. 15.The method according to claim 14 wherein the arthropathy is caused by orassociated with rheumatoid arthritis, spondylitis, gouty arthritis,osteoarthritis, tendonitis, bursitis, acute arthritis, non-rheumatoidarthritis, or gout.
 16. A method for slowing the progression ofarthropathy in a subject comprising administering to the subject acompound of formula I as defined in claim 1, or a pharmaceuticallyacceptable salt thereof.
 17. The method according to claim 16 whereinthe arthropathy is rheumatoid arthritis.
 18. A method for promotingwound healing in a subject comprising administering to the subject acompound of formula I as defined in claim 1, or a pharmaceuticallyacceptable salt thereof.
 19. The method according to any one of claims 1or 16 wherein the compound administered is a compound having increasedbioavailability in comparison with a second medicament, said secondmedicament having as active ingredient a compound of Formula IV, or apharmaceutically acceptable salt thereof,

wherein R1 is as defined in claim 1, and wherein R1 of the secondmedicament is the same as R1 of the improved medicament.
 20. The methodaccording to any one of claims 1 or 16 wherein the compound administeredis a compound having increased half-life in comparison with a secondmedicament, said second medicament having as active ingredient acompound of Formula IV, or a pharmaceutically acceptable salt thereof,

wherein R1 is as defined in claim 1, and wherein R1 of the secondmedicament is the same as R1 of the improved medicament.
 21. A compoundhaving the Formula III, or a pharmaceutically acceptable salt thereof,

wherein R6 is selected from OR4, NR4R5, CN, SR4 or R4; wherein R4 and R5are as defined in claim 1; with the proviso that NR4R5 is not NH₂,NHphenyl or NHpentyl; and with the proviso that R4 is not methyl,propyl, isopropyl, phenyl or CCCH₂OH.
 22. A compound according to claim21 selected from:(2R,3R,4R,5R)-5-(6-amino-2-methoxy-9H-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-[6-amino-2-(2,2-difluoroethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-[6-amino-2-(cyclopentylmethoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-{6-amino-2-[(2,2,3,3-tetrafluorocyclobutyl)oxy]-9H-purin-9-yl}-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-[6-amino-2-(2,5-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-[6-amino-2-(3,4-difluorophenoxy)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-[6-amino-2-[4-chloro-3-(trifluoromethyl)phenoxy]-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;(2R,3R,4R,5R)-5-(6-amino-2-{[(1S)-1-methylpropyl]amino}-9-purin-9-yl)-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol;and(2R,3R,4R,5R)-5-[6-amino-2-(cyclohexylamino)-9H-purin-9-yl]-2-(hydroxymethyl)-4-methoxytetrahydrofuran-3-ol.23. A method for the prevention, treatment, or amelioration of apathological condition that can be improved or prevented by agonism ofadenosine A2A receptors in a subject comprising administering to thesubject an effective amount of a compound according to claim 21 or 22.24. A pharmaceutical formulation containing a compound according toclaim 21 or 22 as active ingredient, in combination with apharmaceutically acceptable carrier, excipient, or diluent.
 25. Apharmaceutical formulation according to claim 24 further comprising anadditional therapeutic agent for use in the prevention, treatment, oramelioration of a pathological condition that can be improved orprevented by agonism of adenosine A2A receptors.
 26. The pharmaceuticalformulation according to claim 25 wherein the additional therapeuticagent is useful for treating pain, inflammation and/or arthropathy.